tag:theconversation.com,2011:/us/topics/reinfection-91931/articlesReinfection – The Conversation2024-01-23T06:51:20Ztag:theconversation.com,2011:article/2213982024-01-23T06:51:20Z2024-01-23T06:51:20ZHow long does immunity last after a COVID infection?<figure><img src="https://images.theconversation.com/files/570785/original/file-20240123-17-tcgvhd.jpg?ixlib=rb-1.1.0&rect=8%2C0%2C5529%2C3686&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/adult-man-lies-on-couch-home-1946857264">Kazantseva Olga/Shutterstock</a></span></figcaption></figure><p>Nearly four years into the pandemic, Australia, like many other countries, is still seeing large numbers of <a href="https://nindss.health.gov.au/pbi-dashboard/">COVID cases</a>. Some 860,221 infections were recorded around the country in 2023, while 30,283 cases have already been reported in 2024. </p>
<p>This is likely to be a significant underestimate, with fewer people testing and reporting than earlier in the pandemic. But the signs suggest parts of Australia are experiencing yet <a href="https://www.abc.net.au/news/2024-01-23/covid-19-case-numbers-from-australia-states-and-territories/103374656">another COVID surge</a>. </p>
<p>While some lucky people claim to have never had COVID, many are facing our second, third or even fourth infection, often despite having been vaccinated. You might be wondering, how long does immunity last after a previous infection or vaccination?</p>
<p>Let’s take a look at what the evidence shows.</p>
<h2>B cells and T cells</h2>
<p>To answer this question, we need to understand a bit about how <a href="https://theconversation.com/what-happens-in-our-body-when-we-encounter-and-fight-off-a-virus-like-the-flu-sars-cov-2-or-rsv-207023">immunity</a> to SARS-CoV-2 (the virus that causes COVID) works. </p>
<p>After being infected or vaccinated, the immune system develops specific antibodies that can neutralise SARS-CoV-2. B cells remember the virus for a period of time. In addition, the immune system produces memory T cells that can kill the virus, and remain in the blood for some months after the clearance of the infection or a vaccination.</p>
<p>A <a href="https://www.science.org/doi/full/10.1126/science.abf4063?rfr_dat=cr_pub++0pubmed&url_ver=Z39.88-2003&rfr_id=ori%3Arid%3Acrossref.org">2021 study</a> found 98% of people had antibodies against SARS-CoV-2’s spike protein (a protein on the surface of the virus that allows it to attach to our cells) one month after symptom onset. Six to eight months afterwards, 90% of participants still had these neutralising antibodies in their blood.</p>
<p>This means the immune system should have recognised and neutralised the same SARS-CoV-2 variant if challenged within six to eight months (if an infection occurred, it should have resulted in mild to no symptoms).</p>
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<a href="https://theconversation.com/what-happens-in-our-body-when-we-encounter-and-fight-off-a-virus-like-the-flu-sars-cov-2-or-rsv-207023">What happens in our body when we encounter and fight off a virus like the flu, SARS-CoV-2 or RSV?</a>
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<h2>But what about when the virus mutates?</h2>
<p>As we know, SARS-CoV-2 has mutated over time, leading to the emergence of new variants such as alpha, beta, delta and omicron. Each of these variants carries mutations that are new to the immune system, even if the person has been previously infected with an earlier variant. </p>
<p>A new variant likely won’t be <a href="https://www.science.org/doi/10.1126/science.adj0070">perfectly recognised</a> – or even <a href="https://www.cell.com/cell/pdf/S0092-8674(21)01578-6.pdf">recognised at all</a> – by the already activated memory T or B cells from a previous SARS-CoV-2 infection. This could explain why people can be so readily reinfected with COVID.</p>
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<img alt="A close up of a person performing a RAT." src="https://images.theconversation.com/files/570803/original/file-20240123-21-9mk3k7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/570803/original/file-20240123-21-9mk3k7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/570803/original/file-20240123-21-9mk3k7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/570803/original/file-20240123-21-9mk3k7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/570803/original/file-20240123-21-9mk3k7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/570803/original/file-20240123-21-9mk3k7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/570803/original/file-20240123-21-9mk3k7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">COVID reinfections are common.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/close-person-using-coronavirus-covid19-rapid-1969543405">Ink Drop/Shutterstock</a></span>
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<p>A recent <a href="https://www.thelancet.com/article/S0140-6736(22)02465-5/fulltext#seccestitle10">review of studies</a> published up to the end of September 2022 looked at the protection conferred by previous SARS-CoV-2 infections.</p>
<p>The authors found a previous infection provided protective immunity against reinfection with the ancestral, alpha, beta and delta variants of 85.2% at four weeks. Protection against reinfection with these variants remained high (78.6%) at 40 weeks, or just over nine months, after the previous infection. This protection decreased to 55.5% at 80 weeks (18 months), but the authors noted there was a lack of data at this time point. </p>
<p>Notably, an earlier infection provided only 36.1% protection against a reinfection with omicron BA.1 at 40 weeks. Omicron has been described as an <a href="https://www.nature.com/articles/s41564-022-01143-7">immune escape variant</a>.</p>
<p>A prior infection showed a high level of protection against severe disease (above 88%) up to 40 weeks regardless of the variant a person was reinfected with.</p>
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Read more:
<a href="https://theconversation.com/there-are-still-good-reasons-to-avoid-catching-covid-again-for-one-your-risk-of-long-covid-goes-up-each-time-196041">There are still good reasons to avoid catching COVID again – for one, your risk of long COVID goes up each time</a>
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<h2>What about immunity after vaccination?</h2>
<p>So far almost 70 million COVID vaccines <a href="https://www.health.gov.au/topics/covid-19/reporting">have been administered</a> to more than <a href="https://www.health.gov.au/resources/publications/covid-19-vaccine-rollout-update-12-january-2023?language=en">22 million people</a> in Australia. Scientists estimated COVID vaccines prevented around <a href="https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(22)00320-6/fulltext">14.4 million deaths</a> in 185 countries in the first year after they became available.</p>
<p>But we know COVID vaccine effectiveness wanes over time. A <a href="https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2804451?utm_source=For_The_Media&utm_medium=referral&utm_campaign=ftm_links&utm_term=050323">2023 review</a> found the original vaccines were 79.6% and 49.7% effective at protecting against symptomatic delta infection at one and nine months after vaccination respectively. They were 60.4% and 13.3% effective against symptomatic omicron at the same time points.</p>
<p>This is where booster doses come into the picture. They’re important to keep the immune system ready to fight off the virus, particularly for those who are more vulnerable to the effects of a COVID infection. </p>
<p>Plus, regular booster doses can provide immunity against different variants. COVID vaccines are constantly being <a href="https://mvec.mcri.edu.au/references/covid-19/">reviewed and updated</a> to ensure optimal protection against <a href="https://www.who.int/activities/tracking-SARS-CoV-2-variants">current circulating strains</a>, with the latest shot available designed to target <a href="https://www.health.gov.au/ministers/the-hon-mark-butler-mp/media/new-covid-19-vaccines-available-to-target-current-variants">the omicron variant XBB 1.5</a>. This is similar to how we approach seasonal flu vaccines.</p>
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<img alt="A woman coughing at her desk." src="https://images.theconversation.com/files/570795/original/file-20240123-19-6v7f8u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/570795/original/file-20240123-19-6v7f8u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/570795/original/file-20240123-19-6v7f8u.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/570795/original/file-20240123-19-6v7f8u.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/570795/original/file-20240123-19-6v7f8u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/570795/original/file-20240123-19-6v7f8u.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/570795/original/file-20240123-19-6v7f8u.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">COVID immunity wanes over time – both from infection and vaccination.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/sick-african-american-girl-working-home-1109017139">Diego Cervo/Shutterstock</a></span>
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<p>A <a href="https://www.nature.com/articles/s41598-023-50335-6">recent study</a> showed a COVID vaccination provides longer protection against reinfection than natural protection alone. The median time from infection to reinfection in non-vaccinated people was only six months, compared with 14 months in people who had received one, two or three doses of vaccine after their first infection. This is called <a href="https://www.science.org/doi/10.1126/science.abj2258">hybrid immunity</a>, and other research has similarly found it provides better protection than natural infection alone.</p>
<p>It also seems timing is important, as receiving a vaccine too soon after an infection (less than six months) appears to be <a href="https://www.nature.com/articles/s41598-023-50335-6">less effective</a> than getting vaccinated later.</p>
<h2>What now?</h2>
<p>Everyone’s immune system is slightly unique, and SARS-CoV-2 continues to mutate, so knowing exactly how long COVID immunity lasts is complicated. </p>
<p>Evidence suggests immunity following infection should generally last six months in healthy adults, and can be prolonged with vaccination. But there are exceptions, and all of this assumes the virus has not mutated so much that it “escapes” our immune response.</p>
<p>While many people feel the COVID pandemic is over, it’s important we don’t forget the lessons we have learned. Practices such as wearing a mask and staying home when unwell can reduce the spread of many viruses, not only <a href="https://www.bmj.com/content/375/bmj-2021-068302">COVID</a>.</p>
<p>Vaccination is not mandatory, but for older adults eligible for a booster under the <a href="https://www.health.gov.au/news/atagi-update-on-the-covid-19-vaccination-program">current guidelines</a>, it’s a very good idea.</p><img src="https://counter.theconversation.com/content/221398/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Lara Herrero receives funding from NHMRC. </span></em></p><p class="fine-print"><em><span>Wesley Freppel does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>While some lucky people believe they’ve never had COVID, many are facing their second, third or even fourth infection. Here’s what the evidence shows.Lara Herrero, Research Leader in Virology and Infectious Disease, Griffith UniversityWesley Freppel, Research Fellow, Institute for Glycomics, Griffith UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2000442023-02-17T14:27:30Z2023-02-17T14:27:30ZHow much immunity do we get from a COVID infection? Large study offers new clues<figure><img src="https://images.theconversation.com/files/510863/original/file-20230217-452-9keo34.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C3761%2C2503&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/variety-passengers-ride-subway-car-1879740988">SmartPhotoLab/Shutterstock</a></span></figcaption></figure><p>After a COVID infection, whether it’s a first, second, or even a third, many of us wonder how long we might be protected against a reinfection, and whether we’ll be susceptible to new variants. Also, if we do catch COVID again, will the immunity we’ve acquired from this infection reduce the severity of the next one?</p>
<p>A <a href="https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(22)02465-5/fulltext">new study</a> published in The Lancet set out to answer these questions, looking at the strength and duration of natural immunity by COVID variant.</p>
<p>The authors collected data from 65 studies across 19 countries, making it the largest review on this topic to date. These studies compared COVID risk among people who had been infected previously and those without a prior infection. Studies looking at natural immunity in combination with vaccination (hybrid immunity) were excluded.</p>
<p>The researchers aimed to assess if infection induced similar protection against reinfection with different variants, and if this waned differently over time.</p>
<p>The analyses spanned studies from the beginning of the pandemic until September 2022, and looked primarily at the alpha, beta, delta and omicron BA.1 variants. </p>
<h2>Protection from reinfection</h2>
<p>The authors evaluated protection against reinfection, symptomatic disease, and severe disease (defined as hospitalisation or death) separately. </p>
<p>They found previous infection was highly protective against reinfection with alpha, beta and delta variants, but less so against omicron BA.1. A previous infection provided moderate protection from reinfection with omicron BA.1 (45%), compared with stronger protection against pre-omicron variants (82%). This was also the case for symptomatic infection. </p>
<p>Data from long-term studies showed that protection against reinfection for pre-omicron variants dropped to 78.6% over 40 weeks, whereas for omicron BA.1 it dropped more rapidly to 36.1%.</p>
<p>When assessing severe disease, however, all variants showed sustained protection above 88% for 40 weeks. This isn’t to say that protection drops substantially after 40 weeks. Rather, it seems there was limited data available that followed people for long enough for the authors to be able to draw strong conclusions beyond this time frame.</p>
<p>The results also revealed that protection against severe disease after natural infection was comparable to that received from two vaccine doses, for both pre-omicron and omicron BA.1 variants.</p>
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Read more:
<a href="https://theconversation.com/genetics-might-explain-why-some-people-have-never-had-covid-but-we-shouldnt-be-too-focused-on-finding-out-198108">Genetics might explain why some people have never had COVID – but we shouldn't be too focused on finding out</a>
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<h2>Making sense of the findings</h2>
<p>A couple of years is a long time for highly contagious respiratory viruses, and SARS-CoV-2 (the virus that causes COVID) has been no different. It has generated sequential variants of concern, with increased transmissibility and capacity to evade our immune responses compared with the ancestral virus. </p>
<p>The study’s observations, which treat protection against pre-omicron variants and omicron BA.1 separately, make sense when we consider how <a href="https://www.nature.com/articles/s41586-022-04474-x">omicron variants differ</a> from their predecessors. </p>
<p>By way of background, neutralising antibodies generated after previous viral infection are important to prevent subsequent virus entry to susceptible cells. These Y-shaped molecules recognise intact proteins of the virus exterior and attach to them, preventing the virus from latching on to the cell receptor necessary for infection. </p>
<p>But to persist, viruses like SARS-CoV-2 introduce random mutations in their genome when they replicate, aiming to continuously alter their proteins to escape immune recognition.</p>
<p>Omicron lineages have enough mutations to differentiate substantially from previous variants, and therefore <a href="https://www.cell.com/cell/fulltext/S0092-8674(21)01578-6?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0092867421015786%3Fshowall%3Dtrue">evade existing antibodies</a>. Evasion from neutralising antibodies explains our failure to control reinfection by omicron variants. </p>
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<img alt="An illustration of SARS-CoV-2, the virus that causes COVID." src="https://images.theconversation.com/files/510865/original/file-20230217-28-rth3o0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/510865/original/file-20230217-28-rth3o0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/510865/original/file-20230217-28-rth3o0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/510865/original/file-20230217-28-rth3o0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/510865/original/file-20230217-28-rth3o0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/510865/original/file-20230217-28-rth3o0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/510865/original/file-20230217-28-rth3o0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">SARS-CoV-2 has evolved significantly.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/sarscov2-coronavirus-virus-which-causes-covid19-1687909633">Kateryna Kon/Shutterstock</a></span>
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<p>Thankfully, we don’t just rely on antibodies for protection. A type of immune cells called <a href="https://www.nature.com/articles/s41590-021-01122-w">T cells</a> recognise snippets of virus proteins rather than intact proteins. This means it would take many more mutations in the virus genome to completely evade T cell immunity. </p>
<p>Unlike antibodies, T cells don’t seek out viruses. Instead they recognise infected cells and rapidly eliminate them to reduce virus factories in the body. T cells therefore act where neutralising antibodies may have failed, after infection. A robust T cell response to coronaviruses is crucial to prevent severe disease, and fortunately, tougher for omicron to evade. </p>
<p>SARS-CoV-2-specific T cells <a href="https://onlinelibrary.wiley.com/doi/10.1111/imr.13089">wane more slowly</a> than antibodies. In fact, people infected with the similar coronavirus SARS in 2003 <a href="https://www.nature.com/articles/s41586-020-2550-z">still had T cells</a> which recognise SARS-CoV-2 17 years after infection.</p>
<h2>Infection versus vaccination</h2>
<p>While a natural infection may offer equivalent protection to vaccination, this is not to say you should seek to become infected. SARS-CoV-2 remains a dangerous and unpredictable virus which can, in some cases, cause a host of damaging effects that linger long after recovery.</p>
<p>The authors suggest a person’s previous infection status and timing should be considered alongside their booster vaccinations to predict protection. However, this may be difficult to implement as infection surveillance has decreased in most countries compared with earlier in the pandemic. In any case, <a href="https://commission.europa.eu/strategy-and-policy/coronavirus-response/safe-covid-19-vaccines-europeans/eu-digital-covid-certificate_en">COVID certificates</a> are used less commonly now.</p>
<p>They also suggest their findings could be used to inform the optimal timing for booster vaccination strategies. That is, there’s probably merit in waiting some time after an infection before getting a booster.</p>
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Read more:
<a href="https://theconversation.com/covid-reinfections-could-be-more-severe-for-some-but-overall-evidence-doesnt-give-us-cause-for-concern-185732">COVID reinfections could be more severe for some – but overall evidence doesn't give us cause for concern</a>
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<p>Further high quality, long-term follow up studies will be important to supplement these findings, as the authors acknowledge there are not as many studies on natural infection compared with protection after vaccination. There were also few studies mapping protection against newer omicron sublineages. As the pandemic continues, there remains much to learn about immune protection against this evolving virus.</p><img src="https://counter.theconversation.com/content/200044/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Zania Stamataki receives funding from the Medical Research Foundation and Innovate UK. She collaborates with AstraZeneca on projects unrelated to topics in this article. </span></em></p>Previous infection was highly protective against reinfection with alpha, beta and delta variants, but less so against omicron BA.1.Zania Stamataki, Associate Professor in Viral Immunology, University of BirminghamLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1965702022-12-19T19:01:08Z2022-12-19T19:01:08ZWith COVID on the rise again, here are some simple steps to help us socialise safely during the holidays<figure><img src="https://images.theconversation.com/files/501784/original/file-20221219-26-e59g6c.jpg?ixlib=rb-1.1.0&rect=0%2C431%2C5760%2C2914&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock/Pressmaster</span></span></figcaption></figure><p>New Zealand’s third wave of COVID infections will likely reach its peak during the holiday period and stretch well into 2023. </p>
<p>The risk of infection is now the highest since June 2022 and continues to rise, driven by new, immune-evasive variants and the social mixing that comes with reduced pandemic controls, end-of-year events and holidays. </p>
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<p>Reported cases have risen almost five-fold from a low point of about 1,300 a day in September to <a href="https://www.rnz.co.nz/news/in-depth/450874/covid-19-data-visualisations-nz-in-numbers">more than 6,000 a day now</a>. Because of declining testing and reporting, the true number of infections is likely <a href="https://www.stuff.co.nz/national/explained/130538183/explainer-how-many-covid19-infections-really-are-out-there">two to three times higher</a>. Hospitalisations are also at their <a href="https://www.rnz.co.nz/news/in-depth/450874/covid-19-data-visualisations-nz-in-numbers">highest level since August</a> and are rising quickly. </p>
<p>The risk of being exposed to the virus has increased markedly in all social settings. For example, in a small gathering of ten people, the probability that one or more of the people attending has the virus has increased from 2-3% to more like 15% currently, and is likely to peak at around 20%. </p>
<p>For large gatherings of 100 people, this risk has risen from about 20% to more than 70%. </p>
<p>The main message is that multiple meetings with different people add up to a lot of potential exposure to this virus, and the risk rises with the number of people and the prevalence of infection (as illustrated by this <a href="https://public.flourish.studio/visualisation/10573093/">infographic</a>). This combination is making the pre-Christmas period particularly high risk for New Zealanders.</p>
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Read more:
<a href="https://theconversation.com/with-a-covid-variant-soup-looming-new-zealand-urgently-needs-another-round-of-vaccine-boosters-193616">With a COVID 'variant soup' looming, New Zealand urgently needs another round of vaccine boosters</a>
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<h2>Risk management</h2>
<p>The good news is that despite widespread COVID infection there are simple ways you can protect yourself and others. A good first step is to recognise that all of us are vulnerable, even if we have been infected previously. </p>
<p>We estimate that more than half of current infections are reinfections, with the <a href="https://covid19.govt.nz/testing-and-isolation/if-you-have-covid-19/after-you-have-had-covid-19">risk starting within a few weeks</a> of each infection and increasing over time. </p>
<p>The most effective way to protect yourself from severe illness is being up to date with vaccines and boosters. A large number of eligible New Zealanders have <a href="https://www.rnz.co.nz/news/national/480692/covid-19-boosters-flatlining-as-case-numbers-surge-across-country">still not had their third and fourth doses</a>. </p>
<p>Anyone who has not been infected in the past three months should check whether they are <a href="https://www.health.govt.nz/covid-19-novel-coronavirus/covid-19-vaccines/covid-19-vaccine-boosters">eligible for a booster</a>.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1602840697500880896"}"></div></p>
<p>After that, it is important to recognise that COVID transmits most effectively in <a href="https://www.who.int/news-room/questions-and-answers/item/coronavirus-disease-covid-19-how-is-it-transmitted">crowded, close-contact, confined indoor environments </a>. Try to avoid these situations. But if you are in packed shopping malls, on buses or planes, <a href="https://www.cdc.gov/mmwr/volumes/71/wr/mm7106e1.htm">wear a respirator style mask</a> (N95, KN95, P2, FFP2). </p>
<p>Such masks provide good protection for the wearer and those around them. They can reduce the risk of transmission by <a href="https://www.pnas.org/doi/full/10.1073/pnas.2110117118">more than 200-fold</a> if both you and the people you are interacting with are wearing them. </p>
<p>When organising events or gatherings, remember that <a href="https://blogs.otago.ac.nz/pubhealthexpert/ventilation-in-nz-schools-during-the-omicron-wave-results-from-a-preliminary-study/">good ventilation is key</a> to preventing transmission. Outdoors is best, but indoors can be relatively safe if well ventilated and not crowded. To add an extra layer of protection, especially when meeting vulnerable people, everyone can take a Rapid Antigen Test (RAT) before attending. </p>
<p>Te Pūnaha Matatini provides useful <a href="https://www.tepunahamatatini.ac.nz/our-values/safe-covid-19-events/">guidelines for organising safe events</a>. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/were-entering-a-new-phase-of-covid-where-we-each-have-to-assess-and-mitigate-our-own-risk-but-how-195912">We're entering a new phase of COVID, where we each have to assess and mitigate our own risk. But how?</a>
</strong>
</em>
</p>
<hr>
<p>If you do get sick, it is <a href="https://covid19.govt.nz/testing-and-isolation/if-you-have-covid-19/">vital to self-isolate</a> and not go to work and social events for a minimum of seven days. RATs are still free, widely available and useful for showing when you are infectious. It can take a few days after the start of an infection to test positive on a RAT so <a href="https://www.fda.gov/medical-devices/safety-communications/home-covid-19-antigen-tests-take-steps-reduce-your-risk-false-negative-results-fda-safety">continue to test</a> after developing symptoms, or after a possible exposure event, even if you initially test negative. </p>
<p>It is also valuable to <a href="https://www.thelancet.com/journals/lanres/article/PIIS2213-2600(22)00226-0/fulltext">test at the end of the seven-day isolation period</a> to check that you are no longer positive and potentially infectious to those around you. </p>
<p>Risk management is a partnership between individuals, their families, employers, venue operators, businesses and other organisations. The other partner is the government, which has a vital role in <a href="https://www.nzherald.co.nz/nz/reintroduction-of-covid-response-measures-urged-amid-third-wave/CDE3UISIZFHO3JRGMH3VWEFJJA/">coordinating and guiding the public health response</a>. </p>
<h2>The future</h2>
<p>After three years, COVID remains a pandemic. It has not yet transitioned to being a predictable endemic infection. </p>
<p><a href="https://esr2.cwp.govt.nz/assets/HEALTH-CONTENT/COVID-Genomics-Insights-Dashboard-CGID/CGID_29_Report.pdf">Genomic surveillance</a> shows a succession of new subvariants replacing those that came before because of their improved ability to evade our immunity. In the last week, BA.5, which has been dominant for more than six months, has been replaced by a collection of BA.2.75 subvariants as the most common in New Zealand. </p>
<p>Ongoing viral evolution and waning immunity means people are being infected multiple times in a single year. Each infection carries a risk of <a href="https://www.nature.com/articles/s41591-022-02051-3">serious illness and long COVID</a>.</p>
<p>The World Health Organization <a href="https://healthpolicy-watch.news/who-director-general-covid-global-health-emergency-can-be-declared-over-in-2023/">suggests</a> the pandemic may cease to be a public health emergency of international concern next year. Regardless of its designation, it is likely to continue as a major health threat. </p>
<p>It has become the <a href="https://www.rnz.co.nz/news/national/480620/covid-19-vs-the-flu-death-rates-compared">second leading cause of death</a> in New Zealand this year (after ischaemic heart disease). Potentially, its largest health impact may be as a <a href="https://www.thelancet.com/journals/eclinm/article/PIIS2589-5370(22)00491-6/fulltext">cause of long-term illness and disability</a> through long COVID. We still need measures to minimise both infections and severe outcomes.</p>
<p>Socialising with whānau, friends and colleagues is a highlight of the holiday season and vital for our health, wellbeing and enjoyment of life. At the same time, relatively small adjustments in how we do these things can help us enjoy the holiday period in relative safety.</p><img src="https://counter.theconversation.com/content/196570/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Michael Baker's employer receives funding for his research on Covid-19 and other infectious diseases from the Health Research Council of New Zealand (HRC) and the New Zealand Ministry of Health.</span></em></p><p class="fine-print"><em><span>David Welch has received funding from HRC, MBIE, and ESR for Covid-19 modeling and genomic analysis.</span></em></p><p class="fine-print"><em><span>Dion O'Neale's employer receives funding from the Health Research Council of New Zealand and from the New Zealand Ministry of Health for his research on COVID-19 modelling and the equity impacts of contagion modelling. </span></em></p>The pre-Christmas period puts New Zealanders at high risk of exposure to COVID. Even at small gatherings of ten people, the probability someone has the virus has increased from 2-3% to about 15%.Michael Baker, Professor of Public Health, University of OtagoDavid Welch, Senior Lecturer, University of Auckland, Waipapa Taumata RauDion O'Neale, Project Lead - COVID Modeling Aotearoa; Senior Lecturer - Department of Physics, University of Auckland; Principal Investigator - Te Pūnaha Matatini, University of Auckland, Waipapa Taumata RauLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1878252022-09-20T05:08:22Z2022-09-20T05:08:22ZNew cases of severe long COVID appear to be dropping – and vaccination is probably key<figure><img src="https://images.theconversation.com/files/482133/original/file-20220831-17-z2dv88.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C6720%2C4466&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/insomnia-drowsy-latin-woman-lie-on-1953915853">fizkes/Shutterstock</a></span></figcaption></figure><p>The term “<a href="https://www.cdc.gov/coronavirus/2019-ncov/long-term-effects/index.html">long COVID</a>” is used to describe symptoms or illness that continue for more than four weeks after a positive COVID test or the original onset of symptoms. Some examples include an ongoing <a href="https://www.bmj.com/content/378/bmj-2021-069503#:%7E:text=Conclusions%20A%20substantial%20proportion%20of,growing%20burden%20of%20long%20covid.">loss of taste or smell</a>, debilitating <a href="https://www.who.int/europe/news/item/09-08-2022-a-life-altered-by-long-covid---susan-s-experience">fatigue</a>, and even sustained damage to <a href="https://jamanetwork.com/journals/jama/fullarticle/2789793">the heart</a> or <a href="https://theconversation.com/we-studied-how-covid-affects-mental-health-and-brain-disorders-up-to-two-years-after-infection-heres-what-we-found-188918">brain</a>.</p>
<p>Long COVID can seriously affect people’s quality of life and ability to work. And there are no proven treatments, meaning that we may be facing a wave of disabilities with little we can do to help.</p>
<p>But in <a href="https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciac630/6652885">a new paper</a>, my colleagues and I report that referrals for more severe cases of long COVID have dropped over the past year, despite large waves of delta and omicron infections. </p>
<p>In this research, we looked at referrals to the long COVID clinic at the Cambridge University Teaching Hospital between August 2020 and June 2022. These patients are on the more severe end of the long COVID symptom spectrum, having been referred following assessment by a team of specialists after at least five months of symptoms.</p>
<p>We found a 79% drop in the number of patients being referred to the clinic from August 2021 to June 2022, compared with August 2020 to July 2021.</p>
<p>Our study is naturally limited by its small size. It includes data from only 145 patients, and these people are local to the area around Cambridge. I’m looking forward to seeing whether other research groups from clinics around the world are seeing similar trends. </p>
<h2>Vaccination and long COVID</h2>
<p>There could be other reasons for the positive trend that we’ve witnessed, but the timing suggests that vaccination is the most likely explanation. The decrease in referrals begins in August 2021, around five months after the British population started receiving second doses of COVID-19 vaccines.</p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/482510/original/file-20220902-22-l8cgn9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/482510/original/file-20220902-22-l8cgn9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=898&fit=crop&dpr=1 600w, https://images.theconversation.com/files/482510/original/file-20220902-22-l8cgn9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=898&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/482510/original/file-20220902-22-l8cgn9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=898&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/482510/original/file-20220902-22-l8cgn9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1129&fit=crop&dpr=1 754w, https://images.theconversation.com/files/482510/original/file-20220902-22-l8cgn9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1129&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/482510/original/file-20220902-22-l8cgn9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1129&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">Based on data from Krishna et al., 2022</span>, <span class="license">Author provided</span></span>
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</figure>
<p>This graph, showing the average number of long COVID referrals before and after this point, highlights a clear link between the two. </p>
<p>There is some evidence already to suggest that immunity gained from vaccination protects against long COVID, though the size of the effect differs <a href="https://www.bmj.com/content/377/bmj-2021-069676">between studies</a>. </p>
<p>For example, <a href="https://www.nature.com/articles/s41591-022-01840-0">one study</a> from the US showed a 15% reduction in long COVID symptoms after vaccination, a study <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8409907/">from the UK</a> saw a 50% reduction, while one study from <a href="https://www.nature.com/articles/s41541-022-00526-5">Israel</a> found vaccination was associated with no long COVID symptoms at all. </p>
<p>The reason for these differences will have a lot to do with testing methods. For instance, how long after COVID-19 did the researchers survey symptoms? What symptoms constitute long COVID, and how severe do these symptoms need to be to qualify?</p>
<p>While it’s difficult to pin down the degree to which vaccination reduces long COVID symptoms, we believe it has played a key role in the reduction in new referrals we’ve seen in our clinic. The fact that other groups, using different measuring techniques, have also observed this association is very reassuring.</p>
<h2>Reinfections</h2>
<p>We’re now in a phase of the pandemic where reinfections are increasingly common and will probably soon constitute most infections.</p>
<p>This leads us to an important question: does reinfection carry the same risk (or even an increased risk) of long COVID, compared with previous infections? If it does, we would be in big trouble as <a href="https://twitter.com/davidsteadson/status/1546308765171224576?s=24&t=wW0DkKTBQzPxxcFJaMPgOw">each reinfection</a> will lead to more and more people with long COVID, eventually overwhelming health services.</p>
<p>But this assumes that previous infections have no bearing on long COVID risk. In reality, we need to consider other factors.</p>
<p>First, there’s the possibility that some people are predisposed (and likewise, not predisposed) to long COVID. Studies have already found <a href="https://www.sciencedirect.com/science/article/pii/S0092867422000721?via%3Dihub">a range of factors</a> that predict long COVID risk, such as previous infections with other viruses, like Epstein-Barr virus.</p>
<p>I haven’t yet seen a study linking long COVID to genetics, but I would be surprised if there are no genetic factors that predispose a person to long COVID.</p>
<p>If some people are indeed predisposed to long COVID, then these people will be more likely to develop long COVID from a first infection, while others will never get long COVID, even after repeated infections. Multiple COVID infections may therefore not be that risky.</p>
<figure class="align-center ">
<img alt="A young man receives a vaccination, while other people wait in the background." src="https://images.theconversation.com/files/482136/original/file-20220831-4924-i1wa60.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/482136/original/file-20220831-4924-i1wa60.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/482136/original/file-20220831-4924-i1wa60.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/482136/original/file-20220831-4924-i1wa60.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/482136/original/file-20220831-4924-i1wa60.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/482136/original/file-20220831-4924-i1wa60.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/482136/original/file-20220831-4924-i1wa60.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Vaccination reduces the risk of long COVID symptoms.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/arabic-man-patient-getting-intramuscular-shot-2067577136">Prostock-studio/Shutterstock</a></span>
</figcaption>
</figure>
<p>Another possibility is that immunity to SARS-CoV-2 (the virus that causes COVID-19) may protect against long COVID. Each subsequent infection would then have a reduced chance of causing long COVID compared with the first infection as immunity builds up. </p>
<p>While the trend we observed would support this (in that a much greater number of COVID cases later on would have been <a href="https://www.ons.gov.uk/peoplepopulationandcommunity/healthandsocialcare/conditionsanddiseases/bulletins/coronaviruscovid19infectionsurveycharacteristicsofpeopletestingpositiveforcovid19uk/20july2022">reinfections</a>), it’s not yet clear if immunity from a prior infection protects against long COVID, nor whether reinfections with SARS-CoV-2 hold the same risk of long COVID as a primary infection. </p>
<p>Research <a href="https://assets.researchsquare.com/files/rs-1749502/v1/499445df-ebaf-4ab3-b30f-3028dff81fca.pdf?c=1655499468">from the US</a> suggests that the risk of long COVID accumulates with every reinfection, so more infections mean higher risk. However, the definition of long COVID in this study is very broad, including any symptoms at six months. It’s also a preprint, meaning the results have not yet been reviewed by other scientists.</p>
<p>The data does suggest, however, that reinfections add less to the risk of long COVID than the initial infection. So while each reinfection is not without risk, the risk may be somewhat less compared with a first infection.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/long-covid-vaccination-could-reduce-symptoms-new-research-suggests-183466">Long COVID: vaccination could reduce symptoms, new research suggests</a>
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</em>
</p>
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<p>We’re certainly not out of the woods yet. We know that immunity to SARS-CoV-2, both from vaccination and prior infections, wanes over time. Long COVID rates may start creeping upwards as immunity across the population drops. We will need to monitor this situation carefully and continue to focus on booster vaccines.</p><img src="https://counter.theconversation.com/content/187825/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ben Krishna does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>A new paper looks at referrals to a long COVID clinic in England over the past two years. The results are good news.Ben Krishna, Postdoctoral Researcher, Immunology and Virology, University of CambridgeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1867332022-07-19T19:23:38Z2022-07-19T19:23:38ZReinfection will be part of the pandemic for months to come. Each repeat illness raises the risk of long COVID<figure><img src="https://images.theconversation.com/files/474460/original/file-20220718-22-bo68et.jpg?ixlib=rb-1.1.0&rect=226%2C26%2C5582%2C1907&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock/Elizaveta Galitckaia</span></span></figcaption></figure><p>The latest Omicron variant BA.5 is fast becoming <a href="https://covid.cdc.gov/covid-data-tracker/#variant-proportions">dominant worldwide</a>, including in New Zealand and Australia. As it continues to surge, reinfection will become increasingly common and this in turn means more people will develop long COVID.</p>
<p>The two most concerning aspects of long COVID are its <a href="https://www.medrxiv.org/content/10.1101/2021.06.28.21259452v1">high prevalence</a> (up to 30% of those infected) and a link between reinfection and a higher risk of harmful outcomes. </p>
<p>American science writer Ed Yong, commenting on <a href="https://www.theatlantic.com/health/archive/2022/06/pandemic-protections/661378/">government responses to the pandemic</a>, described them as a case of débrouillez-vous, which approximates to “you work it out – you’re on your own”. </p>
<p>In the face of official attitudes that are increasingly laissez-faire towards the continuing pandemic, many people no longer take even those precautions over which we have individual control: mask wearing, physical distancing and choosing carefully whether to attend crowded events. The consequences are an increase in both daily case numbers and the lurking burden of long COVID.</p>
<p>Omicron’s first variant, BA.1, emerged in late 2021, substantially different – clinically and genetically – from earlier variants. It displaced the Delta variant and, in early 2022, was itself replaced by BA.2. </p>
<p>The degree to which BA.2 had evolved away from BA.1 is far greater than the genetic distance between the original version of SARS-CoV-2 and the Delta variant. BA.5, a sub-variant of BA.2, is now quickly overtaking other variants. </p>
<figure class="align-center ">
<img alt="Recent data from the US Centers for Disease Control and Prevention show the rapid rise of the BA.5 variant and its replacement of other Omicron variants." src="https://images.theconversation.com/files/474459/original/file-20220718-20-axzkoq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/474459/original/file-20220718-20-axzkoq.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=731&fit=crop&dpr=1 600w, https://images.theconversation.com/files/474459/original/file-20220718-20-axzkoq.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=731&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/474459/original/file-20220718-20-axzkoq.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=731&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/474459/original/file-20220718-20-axzkoq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=919&fit=crop&dpr=1 754w, https://images.theconversation.com/files/474459/original/file-20220718-20-axzkoq.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=919&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/474459/original/file-20220718-20-axzkoq.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=919&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Recent data from the US Centers for Disease Control and Prevention show the rapid rise of the BA.5 variant and its replacement of other Omicron variants.</span>
<span class="attribution"><span class="source">US CDC</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Omicron variants, and BA.5 specifically, show several worrying features. They can evade immunity acquired through <a href="https://www.biorxiv.org/content/10.1101/2022.05.26.493539v1">earlier infections</a> and <a href="https://www.science.org/doi/10.1126/sciimmunol.abq2427">breakthrough infections</a> in <a href="https://www.sciencedirect.com/science/article/pii/S0092867422007103">vaccinated people</a>. BA.5 is better able to infect cells, <a href="https://www.medrxiv.org/content/10.1101/2022.07.07.22277128v1">acting more like Delta</a> than the previous Omicron variants. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/long-covid-affects-1-in-5-people-following-infection-vaccination-masks-and-better-indoor-air-are-our-best-protections-180668">Long COVID affects 1 in 5 people following infection. Vaccination, masks and better indoor air are our best protections</a>
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<h2>What we know about long COVID</h2>
<p>SARS-CoV-2 is not unique in its ability to cause post-acute symptoms and organ damage. <a href="https://www.nature.com/articles/s41591-022-01810-6">Unexplained chronic disability</a> occurred in a minority of patients after Ebola, dengue, polio, the original SARS and West Nile virus infections. </p>
<p>What is different is the sheer size of this pandemic and the number of people affected by long COVID. One of the absolutely critical issues about long COVID is that we should not underestimate it. It is now clear from multiple large studies that:</p>
<ul>
<li><p>It is a set of syndromes</p></li>
<li><p>it affects multiple organs and systems</p></li>
<li><p>it resolves in some but remains persistent in others</p></li>
<li><p>it can be markedly debilitating</p></li>
<li><p>its risk is reduced by vaccination</p></li>
<li><p>its pathology is poorly understood</p></li>
<li><p>we are just beginning to find ways to predict risk and monitor its course</p></li>
<li><p>and management is, at best, ad hoc.</p></li>
</ul>
<p>Perhaps most crucially, reinfection may now become a feature of the pandemic for at least the next 12 to 36 months, raising the risk of long COVID with each repeat infection.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/why-are-there-so-many-new-omicron-sub-variants-like-ba-4-and-ba-5-will-i-be-reinfected-is-the-virus-mutating-faster-182274">Why are there so many new Omicron sub-variants, like BA.4 and BA.5? Will I be reinfected? Is the virus mutating faster?</a>
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</p>
<hr>
<p>Some <a href="https://www.medrxiv.org/content/10.1101/2022.02.27.22271328v1.full.pdf">large studies in Denmark</a>, <a href="https://www.medrxiv.org/content/10.1101/2021.06.28.21259452v1">England</a>, and the <a href="https://www.cdc.gov/mmwr/volumes/71/wr/mm7121e1.htm">US</a> show 20-30% of people who tested positive for COVID-19 experienced at least one post-acute symptom, up to 12 months after infection. Symptoms included loss of smell and taste, fatigue, shortness of breath, reduced limb strength, concentration difficulties, memory disturbance, sleep disturbance and mental or physical exhaustion. </p>
<p>In England, the prevalence of persistent symptoms was <a href="https://theconversation.com/long-covid-female-sex-older-age-and-existing-health-problems-increase-risk-new-research-185911">higher in women and older people</a>. Obesity, smoking or vaping, hospitalisation and deprivation were also associated with a higher probability of persistent symptoms. Those who were hospitalised with COVID in the UK showed even <a href="https://www.bmj.com/content/372/bmj.n693">more severe outcomes</a>. </p>
<figure class="align-center ">
<img alt="A young woman not feeling well." src="https://images.theconversation.com/files/474463/original/file-20220718-40251-tg07xe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/474463/original/file-20220718-40251-tg07xe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=478&fit=crop&dpr=1 600w, https://images.theconversation.com/files/474463/original/file-20220718-40251-tg07xe.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=478&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/474463/original/file-20220718-40251-tg07xe.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=478&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/474463/original/file-20220718-40251-tg07xe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=601&fit=crop&dpr=1 754w, https://images.theconversation.com/files/474463/original/file-20220718-40251-tg07xe.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=601&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/474463/original/file-20220718-40251-tg07xe.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=601&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Long COVID affects all age groups, but younger people have a higher risk for heart-rhythm disturbances.</span>
<span class="attribution"><span class="source">Shutterstock/Starocean</span></span>
</figcaption>
</figure>
<p>In the US, younger survivors were at higher risk than people over 65 for heart-rhythm disturbances and musculo-skeletal pain. This is consistent with other observations that long COVID is not a <a href="https://blogs.otago.ac.nz/pubhealthexpert/long-covid-a-crucial-reason-for-vax-mask-and-distance/#more-19237">disorder only of older age</a>. </p>
<p>However, older survivors had a statistically significantly higher risk of developing certain conditions, including kidney failure, clotting disorders, cerebrovascular disease (stroke), type 2 diabetes, muscle disorders and a variety of neurologic and psychiatric conditions.</p>
<p>A US <a href="https://assets.researchsquare.com/files/rs-1749502/v1/499445df-ebaf-4ab3-b30f-3028dff81fca.pdf?c=1655499468">study</a> involving more than five million people shows the risk of long COVID increases with the number of reinfections. But vaccination consistently <a href="https://ukhsa.koha-ptfs.co.uk/cgi-bin/koha/opac-retrieve-file.pl?id=fe4f10cd3cd509fe045ad4f72ae0dfff">reduces the risk of long COVID</a> as well as severe disease, hospitalisation, ICU and death.</p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/hybrid-immunity-a-combination-of-vaccination-and-prior-infection-probably-offers-the-best-protection-against-covid-183943">Hybrid immunity: a combination of vaccination and prior infection probably offers the best protection against COVID</a>
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</em>
</p>
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<h2>The century-old lesson we’re yet to apply</h2>
<p>There are lessons from the 1918-19 influenza pandemic that we need to bring back into our repertoire, not for a month or two but for the long term.</p>
<p>Japan adopted mask wearing as a key public-health element on a short list of available measures. As science writer Laura Spinney notes in her excellent 2017 coverage of the <a href="https://www.penguin.co.nz/books/pale-rider-9781784702403">flu pandemic’s history</a>, it “probably marked the beginning of the practice of mask wearing to protect others from one’s own germs”. </p>
<p>In Japan, mask use was compulsory for some, such as the police. In some towns, people were not permitted on public transport or allowed to enter a theatre without a mask. Japan had the lowest death rate of all Asian countries in the flu pandemic and is looking to be close to the lowest cumulative mortality in the OECD for the COVID-19 pandemic.</p>
<figure class="align-center ">
<img alt="A couple dressed in kimono and wearing protective face masks walk down deserted stairs at Kiyomizu-dera Temple, a popular tourist destination in Japan." src="https://images.theconversation.com/files/474486/original/file-20220718-12-bdfce9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/474486/original/file-20220718-12-bdfce9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/474486/original/file-20220718-12-bdfce9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/474486/original/file-20220718-12-bdfce9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/474486/original/file-20220718-12-bdfce9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/474486/original/file-20220718-12-bdfce9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/474486/original/file-20220718-12-bdfce9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Mask wearing has protected people in Japan during the flu pandemic a century ago and again now as new Omicron variants continue to surge.</span>
<span class="attribution"><span class="source">Buddhika Weerasinghe/Getty Images</span></span>
</figcaption>
</figure>
<p>During the 1918-19 pandemic, the US, unlike Europe, put considerable effort into public-health interventions, which reduced total mortality. San Francisco, St Louis, Milwaukee and Kansas City had the most effective interventions, <a href="https://www.pnas.org/doi/10.1073/pnas.0611071104">reducing transmission rates by 30-50%</a>.</p>
<p>In historian Geoffrey Rice’s <a href="https://www.canterbury.ac.nz/engage/cup/catalogue/books/black-november-the-1918-influenza-pandemic-in-new-zealand.html">Black November</a> and <a href="https://www.canterbury.ac.nz/alumni/our-alumni/alumni-authors/books/black-flu-1918-the-story-of-new-zealands-worst-public-health-disaster.html">Black Flu</a> (together the most comprehensive coverage of the 1918-19 pandemic in Aotearoa), there are some photographs of people wearing masks and a reference to “gauze masks” for shop keepers. However, there is little evidence to suggest mask wearing was widespread or encouraged in New Zealand. </p>
<p>The influential Italian newspaper <em>Corriere della Sera</em> reported daily death tolls during the 1918-19 flu pandemic until civil authorities asserted it was stirring up anxiety and <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3559034/">forced it to stop</a>. As Spinney notes, people could see the exodus of dead bodies from their neighbourhoods and the silence was provoking even more anxiety. </p>
<p>The pandemic and the silence conspired to confuse people about the efficacy of public-health measures and compliance dropped off even further. People drifted back to church and race meetings – and left masks at home. Public-health infrastructure <a href="https://academic.oup.com/shm/article-abstract/16/1/97/1698888?redirectedFrom=PDF">collapsed</a>.</p>
<p>Vaccines (not available a century ago) are almost all that stands between us and a similar collapse. We would remain stronger and healthier – and reduce the burden of long COVID – if we increased vaccination coverage and universally adopted Japanese-style regular mask use and physical distancing.</p><img src="https://counter.theconversation.com/content/186733/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>John Donne Potter does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>SARS-CoV-2 is not the first virus to cause unexplained chronic illness, but the sheer size of this pandemic means more people will develop long COVID.John Donne Potter, Professor, Research Centre for Hauora and Health, Massey UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1857322022-06-27T12:46:14Z2022-06-27T12:46:14ZCOVID reinfections could be more severe for some – but overall evidence doesn’t give us cause for concern<figure><img src="https://images.theconversation.com/files/470829/original/file-20220624-20-e9a4yf.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5463%2C3637&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/sick-day-home-blonde-woman-has-1785776795">Photoroyalty/Shutterstock</a></span></figcaption></figure><p>The COVID pandemic has been going on for well over two years now. During this time, SARS-CoV-2 (the virus that causes COVID-19) has slowly mutated, allowing it to <a href="https://www.nature.com/articles/s41586-021-04385-3">evade the immune system</a> enough to infect people many times.</p>
<p>As so many of us have had COVID already, it’s no surprise that plenty of people are catching the virus for a second or even a third time. In the UK, this has been <a href="https://coronavirus.data.gov.uk/details/cases?areaType=overview&areaName=United%20Kingdom">particularly noticeable</a> since the emergence of the omicron variant from December 2021 onwards.</p>
<p>But when reinfected, are you likely to feel better or worse than you did the first time you had COVID? As well as being a question many people are curious about, this is an important issue from a public health perspective.</p>
<p>If symptoms are more severe, each time someone gets infected, we would expect the pandemic to escalate as people become sicker and sicker. A zero-COVID strategy would be the only way to avert waves of serious illness. </p>
<p>The alternative is almost precisely the opposite. If each subsequent infection is less severe, the pandemic would eventually fizzle out on its own without the need for masking, quarantine, lockdowns or other measures.</p>
<h2>So what does the evidence say?</h2>
<p>A recent <a href="https://assets.researchsquare.com/files/rs-1749502/v1/499445df-ebaf-4ab3-b30f-3028dff81fca.pdf?c=1655499468">preprint</a> (an article published online before undergoing peer review) was interpreted as suggesting that symptoms of reinfections with COVID are worse than those of initial infections. </p>
<p>But the authors didn’t specifically look at symptom severity. They looked at the likelihood of death from any cause, hospitalisation, and a variety of health problems within six months after infection. The researchers concluded that these measures were worse after reinfections.</p>
<p>While this isn’t good news, the results need to be interpreted carefully. The data used in this study comes from electronic healthcare records of over 5 million US army veterans, over 290,000 of whom had COVID at least once. </p>
<p>For a start, the group studied was already at higher risk of experiencing worse outcomes compared with the overall population. The average age was 60, around 20% smoked and more than 80% of those who contracted COVID were not vaccinated. So the results may not apply to the general population.</p>
<p>Second, the reinfection group were analysed <a href="https://twitter.com/OmicronData/status/1539271825624125441">immediately after</a> reinfection, while the initial infection group were not analysed until 30 days following infection. This means that the outcomes observed for reinfection include all the early COVID symptoms (headache, cough, fatigue and so on) which the other group may have recovered from. As the data included any symptoms or health problems that occurred within the study period, including acute infection in one group skews the findings, making reinfections appear worse. </p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/covid-reinfections-are-they-milder-and-do-they-strengthen-immunity-176592">COVID reinfections: are they milder and do they strengthen immunity?</a>
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<p>So what does this preprint show? It suggests that reinfections increase your general risk of health problems. But it’s worth remembering that the study population was at higher risk already.</p>
<p>Respiratory infections such as <a href="https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2789446">influenza</a> are a <a href="https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)30977-6/fulltext">leading cause</a> of death globally, so it’s not entirely surprising that any extra respiratory infections will increase a person’s risk of health problems.</p>
<p>This finding, however, is not the same as symptoms of reinfections being more severe.</p>
<h2>Immune memory</h2>
<p>This study caused somewhat of a stir on Twitter because we would expect the opposite – that each subsequent infection would tend to cause less severe symptoms than an initial infection, or at least very little change.</p>
<p><a href="https://en.wikipedia.org/wiki/Immunological_memory">Immune memory</a> is the phenomenon where the immune system “remembers” past infections and responds more quickly and effectively to reinfections, lessening the spread of the virus and general symptoms. This is because the immune system makes antibodies, and a type of white blood cell called a T cell during the initial infection. The immune system then reuses the same antibodies and T cells to fight the reinfection. </p>
<p>Many modern vaccines (including COVID vaccines) are based on this concept – they “train” the immune system to remember the virus next time. </p>
<figure class="align-center ">
<img alt="A man blows his nose on the sofa." src="https://images.theconversation.com/files/470830/original/file-20220624-15-npqvo6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/470830/original/file-20220624-15-npqvo6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=380&fit=crop&dpr=1 600w, https://images.theconversation.com/files/470830/original/file-20220624-15-npqvo6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=380&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/470830/original/file-20220624-15-npqvo6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=380&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/470830/original/file-20220624-15-npqvo6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=478&fit=crop&dpr=1 754w, https://images.theconversation.com/files/470830/original/file-20220624-15-npqvo6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=478&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/470830/original/file-20220624-15-npqvo6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=478&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">More and more people are being infected with COVID multiple times.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/middle-age-man-feeling-sick-cold-1806002041">Krakenimages.com/Shutterstock</a></span>
</figcaption>
</figure>
<p>For many diseases, such as <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2610468/">smallpox</a>, <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8189124/">measles</a> and chickenpox, surviving the illness once gives you immunity that makes any reinfection much less severe. One exception is dengue fever where the immune system can make antibodies that actually aid reinfection, <a href="https://en.wikipedia.org/wiki/Antibody-dependent_enhancement#Dengue">making symptoms worse</a> in some cases.</p>
<p>With COVID, studies on reinfections tend to look at deaths and hospitalisations, as these are easier to measure than symptoms. In general, they find that reinfections are <a href="https://www.sciencedirect.com/science/article/pii/S016344532200010X">less severe</a> than initial infections.</p>
<h2>It’s not the same for everyone</h2>
<p>You might be thinking, “my second infection hit me harder than the first”. It is plausible that some people might experience worse symptoms from reinfection compared with initial infection. This could be due to several factors. Different strains might cause more severe symptoms, such as delta, which is <a href="https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/2787492">likely more severe</a> than beta.</p>
<p>A <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7686757/">higher initial dose</a> of virus (say, if someone with COVID sneezes on you) might allow more virus spread before the immune system can control the infection.</p>
<p>Finally, the waning of immune responses over time might lead to worse symptoms. For example, if your first infection occurs very soon after vaccination, but you’re then reinfected months later when your antibody levels are lower, it would make sense that your first infection was milder. </p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/hybrid-immunity-a-combination-of-vaccination-and-prior-infection-probably-offers-the-best-protection-against-covid-183943">Hybrid immunity: a combination of vaccination and prior infection probably offers the best protection against COVID</a>
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<p>These things will happen in individual people but are unlikely to play a major role across large populations. What would concern me is if we started to see trends of hospital admissions among people who had mild symptoms during a first infection but were getting very sick with reinfections. So far, I have seen no evidence of this.</p><img src="https://counter.theconversation.com/content/185732/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ben Krishna does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Intuitively, we would assume that subsequent infections should be less severe. But this won’t always be the case.Ben Krishna, Postdoctoral Researcher, Immunology and Virology, University of CambridgeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1839432022-06-13T14:10:43Z2022-06-13T14:10:43ZHybrid immunity: a combination of vaccination and prior infection probably offers the best protection against COVID<figure><img src="https://images.theconversation.com/files/467770/original/file-20220608-26-46z6ku.jpg?ixlib=rb-1.1.0&rect=0%2C8%2C5991%2C3979&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/antibodies-attacking-sarscov2-virus-corona-covid19-1994643521">Kateryna Kon/Shutterstock</a></span></figcaption></figure><p>When we’re exposed to a pathogen such as a virus, our immune system identifies it as a foreign invader and mounts an attack. This ultimately results in the formation of antibodies which can neutralise the invading pathogen next time we encounter it. </p>
<p>It’s a <a href="https://aacijournal.biomedcentral.com/articles/10.1186/s13223-018-0278-1">complex process</a>. Our immune system forms B cells (that make antibodies) and specialist T cells (that either aid B cells or kill infected cells), as well as memory cells to prepare for any future attacks from the same pathogen. </p>
<p>The pathogen which triggers this process can be introduced through natural infection or vaccination. Of course, after two-and-a-half years of COVID we know neither of these forms of immunity are foolproof. Although prior infection and vaccination both provide some degree of immunity for a time, plenty of people catch COVID after being previously infected, vaccinated, or both.</p>
<p>So which is “better” – the immunity produced from an infection, or a vaccine? Or is a combination of both optimal? Let’s take a look.</p>
<h2>Vaccines vs natural immunity</h2>
<p>When we receive a vaccine, it exposes our immune system to parts of the pathogen, allowing it to form antibodies and memory cells, without the risks of infection. The <a href="https://www.nhs.uk/conditions/coronavirus-covid-19/coronavirus-vaccination/coronavirus-vaccine/">COVID vaccines</a> work in slightly different ways, but all expose our immune system to the spike protein of SARS-CoV-2. This is the protein that coats the virus particle and is essential for infecting our cells.</p>
<p>Our immune response following vaccination is specific to the part of the virus contained in the vaccine. During an infection, our bodies make antibodies against many different areas of the virus – but not all of these antibodies will be equally useful. The current COVID vaccines contain the spike protein because it’s generally accepted that antibodies specific to <a href="https://www.nature.com/articles/nri891">surface proteins</a> are the most protective.</p>
<p>Many viruses have mechanisms to “evade” <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6832425/">the immune system</a>, delaying the identification of the pathogen and modulating how immune cells respond. SARS-CoV-2 is <a href="https://pubmed.ncbi.nlm.nih.gov/34942634/%20https://pubmed.ncbi.nlm.nih.gov/34562466/">no exception</a>, which, in theory, could weaken the immune response generated by an infection.</p>
<p>Vaccines are designed to prompt a very strong immune response. Most vaccines contain “<a href="https://www.cdc.gov/vaccinesafety/concerns/adjuvants.html">adjuvants</a>” – essentially extra ingredients to help our immune systems form a robust response to the spike protein.</p>
<p>A <a href="https://pubmed.ncbi.nlm.nih.gov/35173254/">recent study</a> found that people who were vaccinated against SARS-CoV-2 had antibody levels 17 times higher against the spike protein compared with people who had a natural infection. The same study also showed that antibodies from vaccination were better at preventing viral entry into cells. </p>
<p>Another <a href="https://pubmed.ncbi.nlm.nih.gov/34103407/">study</a> demonstrated that antibodies from the vaccine targeted more areas of the spike protein than those formed against infection.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/can-scientists-predict-all-of-the-ways-the-coronavirus-will-evolve-156673">Can scientists predict all of the ways the coronavirus will evolve?</a>
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</em>
</p>
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<p>But our immunity to pathogens isn’t all about antibodies. An effective <a href="https://www.sciencedirect.com/science/article/pii/S1074761321002168">T cell response</a> <a href="https://pubmed.ncbi.nlm.nih.gov/35105982/">is key</a> in clearing SARS-CoV-2 from the body and preventing severe disease.</p>
<p>Looking at T cells from infection versus vaccination shows some subtle differences. Both produce a similar amount of memory T cells, but people <a href="https://www.sciencedirect.com/science/article/pii/S0092867422003282?via%3Dihub">previously infected</a> with SARS-CoV-2 have more “Th1” T cells. Th1 cells specialise in recognising viruses in our cells and directing the antiviral response. </p>
<p>A range of different types of T cells are needed to fight a viral infection, so it’s currently unclear whether this Th1 cell bias seen in natural infections actually provides greater protection against reinfection.</p>
<figure class="align-center ">
<img alt="A senior woman receives a vaccine." src="https://images.theconversation.com/files/468074/original/file-20220609-16447-xcac9o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/468074/original/file-20220609-16447-xcac9o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=378&fit=crop&dpr=1 600w, https://images.theconversation.com/files/468074/original/file-20220609-16447-xcac9o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=378&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/468074/original/file-20220609-16447-xcac9o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=378&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/468074/original/file-20220609-16447-xcac9o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=475&fit=crop&dpr=1 754w, https://images.theconversation.com/files/468074/original/file-20220609-16447-xcac9o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=475&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/468074/original/file-20220609-16447-xcac9o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=475&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Vaccination triggers an immune response.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/doctor-giving-senior-woman-vaccination-virus-1898539783">Yuganov Konstantin/Shutterstock</a></span>
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</figure>
<p>While measuring immune responses in the form of antibodies and T cells can give us lots of important information, comparing infection rates in people with immunity from infection versus vaccination can tell us which form is more protective against future infections.</p>
<p>A <a href="https://pubmed.ncbi.nlm.nih.gov/35149106/">range of studies</a> that have tracked people over several months reported that patients with a prior infection were roughly five to 20 times less likely to contract COVID compared with their unvaccinated, not previously infected counterparts. </p>
<p>As vaccination only became widely available in mid 2021, long-term data for infection rates post-vaccination is still emerging. But <a href="https://academic.oup.com/aje/advance-article/doi/10.1093/aje/kwac060/6556183?login=false">early studies</a> indicate that immunity from vaccination and infection offer similar protection against SARS-CoV-2 infection.</p>
<h2>Hybrid immunity</h2>
<p>With more people vaccinated and the virus still circulating, many people are developing “hybrid immunity” to SARS-CoV-2: immunity formed from both vaccination and an infection.</p>
<p>Though there are only a handful of studies on this so far, the current consensus is that hybrid immunity is more protective than either vaccination or infection alone. In one study, <a href="https://doi.org/10.1016/S1473-3099(22)00143-8">researchers found</a> that people who had received a single dose of a COVID vaccine and been infected with the virus were 58% less likely to get reinfected compared to people with natural immunity alone. Those with two-dose hybrid immunity had a 66% lower chance of reinfection.</p>
<p>One <a href="https://doi.org/10.1016/S2665-9913(21)00356-8">small study from India</a> showed that a hybrid of a single vaccine dose plus natural infection produced the highest antibody levels compared to either one or two vaccines without infection, or natural immunity alone.</p>
<p>A <a href="https://www.nejm.org/doi/10.1056/NEJMoa2118946">larger study</a> conducted in Israel in 2021 found hybrid immunity was more protective than two vaccine doses or natural immunity alone.</p>
<h2>Limitations</h2>
<p>Through no fault of researchers, when using patients from particular populations, the data will be limited. Factors such as access to healthcare and what vaccines were available and when they were available can differ between populations, and may affect the results, meaning they mightn’t be applicable to all groups.</p>
<p>Meanwhile, immune responses vary between individuals. Factors including age and existing health conditions are known to affect our immune systems. Even things like the <a href="https://www.pnas.org/doi/10.1073/pnas.1905080116">time of day</a> can affect immune responses to vaccines. </p>
<p>A significant limitation is that many of these studies took place before omicron, which has a <a href="https://pubmed.ncbi.nlm.nih.gov/34982466/">highly mutated spike protein</a>. These changes make it less susceptible to the antibodies formed from vaccines (all of which are based on the original Wuhan strain) or previous infections. Indeed, evidence suggests the reinfection rate during the omicron wave has been <a href="https://pubmed.ncbi.nlm.nih.gov/35472367/">much higher</a> than during waves driven by earlier variants. So subsequent studies may produce very different results.</p>
<p>Immunology is a rapidly developing area and there’s still a lot we don’t fully understand. But I personally won’t be seeking out a “natural” infection to boost my immunity against COVID when the <a href="https://pubmed.ncbi.nlm.nih.gov/34817268/">risks of infection</a> far outweigh those of vaccination.</p><img src="https://counter.theconversation.com/content/183943/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Grace C Roberts works for the University of Leeds and receives funding from the MRC. </span></em></p><p class="fine-print"><em><span>Lena Glaser works for Queens University Belfast.</span></em></p>‘Hybrid immunity’ is the term for immunity acquired from both prior infection and vaccination.Grace C Roberts, Research Fellow in Virology, University of LeedsLena Glaser, PhD Candidate, School of Medicine, Dentistry and Biomedical Sciences, Queen's University BelfastLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1822742022-05-05T19:57:54Z2022-05-05T19:57:54ZWhy are there so many new Omicron sub-variants, like BA.4 and BA.5? Will I be reinfected? Is the virus mutating faster?<figure><img src="https://images.theconversation.com/files/461147/original/file-20220504-16-jqvvfw.jpg?ixlib=rb-1.1.0&rect=2%2C1%2C995%2C456&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/mutating-virus-concept-new-coronavirus-b117-1905904402">Shutterstock</a></span></figcaption></figure><p>By now, many of us will be familiar with the Omicron variant of SARS-CoV-2, the virus that causes COVID. This <a href="https://www.who.int/en/activities/tracking-SARS-CoV-2-variants/">variant of concern</a> has changed the course of the pandemic, leading to a dramatic rise in cases around the world.</p>
<p>We are also increasingly hearing about new Omicron sub-variants with names such as BA.2, BA.4 and now BA.5. The concern is these sub-variants may lead to people <a href="https://www.medrxiv.org/content/10.1101/2022.04.29.22274477v1">becoming reinfected</a>, leading to another rise in cases.</p>
<p>Why are we seeing more of these new sub-variants? Is the virus mutating faster? And what are the implications for the future of COVID?</p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/whats-the-difference-between-mutations-variants-and-strains-a-guide-to-covid-terminology-154825">What's the difference between mutations, variants and strains? A guide to COVID terminology</a>
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<h2>Why are there so many types of Omicron?</h2>
<p>All viruses, SARS-CoV-2 included, mutate constantly. The vast majority of mutations have little to no effect on the ability of the virus to transmit from one person to another or to cause severe disease.</p>
<p>When a virus accumulates a substantial number of mutations, it’s considered a <a href="https://cov-lineages.org/index.html">different lineage</a> (somewhat like a different branch on a family tree). But a viral lineage is not labelled a variant until it has accumulated several unique mutations known to enhance the ability of the virus to transmit and/or cause more severe disease. </p>
<p>This was the case for the BA lineage (sometimes known as B.1.1.529) the World Health Organization <a href="https://www.who.int/en/activities/tracking-SARS-CoV-2-variants/">labelled Omicron</a>. Omicron has spread rapidly, representing <a href="https://cov-lineages.org/lineage.html?lineage=B.1.1.529">almost all</a> current cases with genomes sequenced globally. </p>
<p>Because Omicron has spread swiftly, and has had many opportunities to mutate, it has also acquired specific mutations of its own. These have given rise to several sub-lineages, or sub-variants. </p>
<p>The first two were labelled BA.1 and <a href="https://theconversation.com/ba-2-is-like-omicrons-sister-heres-what-we-know-about-it-so-far-176137">BA.2</a>. The current list now also includes BA.1.1, BA.3, BA.4 and BA.5.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/F6zrS6N5jPA?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">What we know about the latest Omicron sub-variants, according to the World Health Organization.</span></figcaption>
</figure>
<p>We did see sub-variants of earlier versions of the virus, such as Delta. However, Omicron has outcompeted these, potentially because of its increased transmissibility. So sub-variants of earlier viral variants are much less common today and there is less emphasis in tracking them.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-does-omicron-compare-with-delta-heres-what-we-know-about-infectiousness-symptoms-severity-and-vaccine-protection-172963">How does Omicron compare with Delta? Here's what we know about infectiousness, symptoms, severity and vaccine protection</a>
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<h2>Why are the sub-variants a big deal?</h2>
<p>There is evidence these Omicron sub-variants – specifically BA.4 and BA.5 – are particularly effective at <a href="https://www.medrxiv.org/content/10.1101/2022.04.29.22274477v1">reinfecting people</a> with previous infections from BA.1 or other lineages. There is also concern these sub-variants may infect people who have been vaccinated.</p>
<p>So we expect to see a <a href="https://www.smh.com.au/national/nsw/tens-of-thousands-of-covid-19-reinfections-likely-in-nsw-as-first-ba-4-case-detected-20220428-p5agta.html">rapid rise in COVID cases</a> in the coming weeks and months due to reinfections, which we are already seeing in South Africa.</p>
<p>However, <a href="https://doi.org/10.1136/bmj-2021-069761">recent research</a> suggests a third dose of the COVID vaccine is the most effective way to slow the spread of Omicron (including sub-variants) and prevent COVID-associated hospital admissions.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1521554451760304129"}"></div></p>
<p>Recently, BA.2.12.1, has also drawn attention because it has been spreading rapidly in the United States and was recently detected in <a href="https://www.abc.net.au/news/2022-04-30/covid-19-omicron-subvariant-ba-2-12-1-detected-in-victoria/101027818">wastewater in Australia</a>. Alarmingly, even if someone has been infected with the Omicron sub-variant BA.1, re-infection is still possible with sub-lineages of <a href="https://www.biorxiv.org/content/10.1101/2022.04.30.489997v1">BA.2, BA.4 and BA.5</a> due to their capacity to evade immune responses. </p>
<h2>Is the virus mutating faster?</h2>
<p>You’d think SARS-CoV-2 is a super-speedy front-runner when it comes to mutations. But the virus actually mutates relatively slowly. Influenza viruses, for example, <a href="https://academic.oup.com/mbe/article/39/2/msac009/6509523?login=false">mutate at least four times faster</a>.</p>
<p>SARS-CoV-2 does, however, have “mutational sprints” for short periods of time, <a href="https://academic.oup.com/mbe/article/39/2/msac013/6509545?login=false">our research shows</a>. During one of these sprints, the virus can mutate four-fold faster than normal for a few weeks.</p>
<p>After such sprints, the lineage has more mutations, some of which may provide an advantage over other lineages. Examples include mutations that can help the virus become more transmissible, cause more severe disease, or evade our immune response, and thus we have new variants emerging.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/461156/original/file-20220504-14-v9wxoo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Sprinter, viewed from behind, crouched down ready to start running" src="https://images.theconversation.com/files/461156/original/file-20220504-14-v9wxoo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/461156/original/file-20220504-14-v9wxoo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/461156/original/file-20220504-14-v9wxoo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/461156/original/file-20220504-14-v9wxoo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/461156/original/file-20220504-14-v9wxoo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/461156/original/file-20220504-14-v9wxoo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/461156/original/file-20220504-14-v9wxoo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Viral mutations speed up in a ‘sprint’ for a few weeks, sometimes leading to new sub-variants.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/one-man-on-start-line-awaits-1384921652">Shutterstock</a></span>
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<p>Why the virus undergoes mutational sprints that lead to the emergence of variants is unclear. But there are <a href="https://www.nature.com/articles/d41586-022-00215-2">two main theories</a> about the origins of Omicron and how it accumulated so many mutations. </p>
<p>First, the virus could have evolved in chronic (prolonged) infections in people who are immunosuppressed (have a weakened immune system).</p>
<p>Second, the virus could have “jumped” to another species, before infecting humans again.</p>
<h2>What other tricks does the virus have?</h2>
<p>Mutation is not the only way variants can emerge. The <a href="https://theconversation.com/whats-the-new-omicron-xe-variant-and-should-i-be-worried-180584">Omicron XE variant</a> appears to have resulted from a recombination event. This is where a single patient was infected with BA.1 and BA.2 at the same time. This coinfection led to a “genome swap” and a hybrid variant.</p>
<figure class="align-center ">
<img alt="Recombination through conifection" src="https://images.theconversation.com/files/461075/original/file-20220503-43085-4rctpc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/461075/original/file-20220503-43085-4rctpc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=396&fit=crop&dpr=1 600w, https://images.theconversation.com/files/461075/original/file-20220503-43085-4rctpc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=396&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/461075/original/file-20220503-43085-4rctpc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=396&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/461075/original/file-20220503-43085-4rctpc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=498&fit=crop&dpr=1 754w, https://images.theconversation.com/files/461075/original/file-20220503-43085-4rctpc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=498&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/461075/original/file-20220503-43085-4rctpc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=498&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Two viruses can ‘swap’ genetic material, resulting in a recombinant virus that can become a distinct lineage (recombinant lineage X).</span>
<span class="attribution"><span class="source">Ashleigh Porter</span></span>
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<p>Other instances of recombination in SARS-CoV-2 have been reported between Delta and Omicron, resulting in what’s been <a href="https://theconversation.com/deltacron-what-scientists-know-so-far-about-this-new-hybrid-coronavirus-179442">dubbed Deltacron</a>.</p>
<p>So far, recombinants do not appear to have higher transmissibility or cause more severe outcomes. But this could change rapidly with new recombinants. So scientists are closely monitoring them. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/should-we-worry-about-the-xe-variant-maybe-not-yet-but-hybrids-will-become-more-frequent-as-covid-evolves-180672">Should we worry about the XE variant? Maybe not yet, but 'hybrids' will become more frequent as COVID evolves</a>
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<h2>What might we see in the future?</h2>
<p>As long as the virus is circulating, we will continue to see new virus lineages and variants. As Omicron is the most common variant currently, it is likely we will see more Omicron sub-variants, and potentially, even recombinant lineages.</p>
<p>Scientists will continue to track new mutations and recombination events (particularly with sub-variants). They will also use genomic technologies to predict how these might occur and any effect they may have on the behaviour of the virus.</p>
<p>This knowledge will help us limit the spread and impact of variants and sub-variants. It will also guide the development of vaccines effective against multiple or specific variants.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/a-single-vaccine-to-beat-all-coronaviruses-sounds-impossible-but-scientists-are-already-working-on-one-156373">A single vaccine to beat all coronaviruses sounds impossible. But scientists are already working on one</a>
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<img src="https://counter.theconversation.com/content/182274/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sebastian Duchene receives funding from the Australian Research Council (DE190100805) and the Australian Medical Research Future Fund (MRF9200006).</span></em></p><p class="fine-print"><em><span>Ashleigh Porter receives funding from the Australian Medical Research Future Fund (MRF9200006).</span></em></p>It’s hard to keep up. But new Omicron sub-variants are emerging that may lead to reinfections and another spike in cases.Sebastian Duchene, ARC DECRA Fellow, The University of MelbourneAsh Porter, Research officer, The Peter Doherty Institute for Infection and ImmunityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1796192022-03-22T16:12:16Z2022-03-22T16:12:16ZWhat is the new COVID-19 variant BA.2, and will it cause another wave of infections in the US?<figure><img src="https://images.theconversation.com/files/453423/original/file-20220321-14981-gwxv7z.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C2448%2C1224&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">BA.2, one of three main omicron sublineages, is sweeping the world.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/new-variant-royalty-free-image/1302316037">BlackJack3D/iStock via Getty Images Plus</a></span></figcaption></figure><p><em>A new omicron subvariant of the virus that causes COVID-19, BA.2, is quickly becoming the predominant source of infections amid rising cases around the world. Immunologists Prakash Nagarkatti and Mitzi Nagarkatti of the University of South Carolina explain what makes it different from previous variants, whether there will be another surge in the U.S. and how best to protect yourself.</em></p>
<h2>What is BA.2, and how is it related to omicron?</h2>
<p>BA.2 is the latest <a href="https://doi.org/10.1038/s41586-022-04411-y">subvariant of omicron</a>, the dominant strain of the SARS-CoV-2 virus that causes COVID-19. While the origin of BA.2 is still unclear, it has quickly become the dominant strain in many countries, including <a href="https://doi.org/10.1126/science.ada1615">India, Denmark and South Africa</a>. It is <a href="https://www.who.int/news/item/08-03-2022-interim-statement-on-covid-19-vaccines-in-the-context-of-the-circulation-of-the-omicron-sars-cov-2-variant-from-the-who-technical-advisory-group-on-covid-19-vaccine-composition-(tag-co-vac)-08-march-2022">continuing to spread</a> in Europe, Asia and many parts of the world.</p>
<p>The omicron variant, officially known as B.1.1.529, of SARS-CoV-2 has <a href="https://www.who.int/publications/m/item/weekly-epidemiological-update-on-covid-19---1-february-2022">three main subvariants</a> in its <a href="https://www.cdc.gov/coronavirus/2019-ncov/variants/variant-classifications.html">lineage</a>: BA.1, BA.2 and BA.3. The earliest omicron subvariant to be detected, BA.1, was first reported in <a href="https://www.cdc.gov/coronavirus/2019-ncov/science/science-briefs/scientific-brief-omicron-variant.html">November 2021 in South Africa</a>. While scientists believe that all the subvariants may have <a href="https://doi.org/10.1038/d41586-022-00215-2">emerged around the same time</a>, BA.1 was <a href="https://www.who.int/publications/m/item/weekly-epidemiological-update-on-covid-19---1-february-2022">predominantly responsible</a> for the winter surge of infections in the Northern Hemisphere in 2021.</p>
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<p>The first omicron subvariant, BA.1, is unique in the number of alterations it has compared to the original version of the virus – it has <a href="https://doi.org/10.1038/s41586-022-04411-y">over 30 mutations</a> in the <a href="https://doi.org/10.1038/s41401-020-0485-4">spike protein</a> that helps it enter cells. Spike protein mutations are of high concern to scientists and public health officials because they affect how infectious a particular variant is and whether it is able to <a href="https://doi.org/10.1038/s41586-021-04385-3">escape the protective antibodies</a> that the body produces after vaccination or a prior COVID-19 infection.</p>
<p>BA.2 has <a href="https://doi.org/10.1056/NEJMc2201849">eight unique mutations</a> not found in BA.1, and <a href="https://doi.org/10.1038/s41586-022-04594-4">lacks 13 mutations</a> that BA.1 does have. BA.2 does, however, share <a href="https://covariants.org/shared-mutations">around 30 mutations</a> with BA.1. Because of its relative genetic similarity, it is considered a <a href="https://www.cdc.gov/coronavirus/2019-ncov/variants/variant-classifications.html">subvariant</a> of omicron as opposed to a completely new variant.</p>
<h2>Why is it called a ‘stealth’ variant?</h2>
<p>Some scientists have called BA.2 a <a href="https://www.ama-assn.org/delivering-care/public-health/what-ba2-or-stealth-omicron-subvariant">“stealth” variant</a> because, unlike the BA.1 variant, it <a href="https://doi.org/10.1136/bmj.n3133">lacks a particular genetic signature</a> that distinguishes it from the delta variant.</p>
<p>While standard <a href="https://www.genome.gov/about-genomics/fact-sheets/Understanding-COVID-19-PCR-Testing">PCR tests</a> are still able to detect the BA.2 variant, they might not be able to tell it apart from the delta variant.</p>
<h2>Is it more infectious and lethal than other variants?</h2>
<p>BA.2 is considered to be <a href="https://doi.org/10.1038/d41586-022-00471-2">more transmissible</a> but not more <a href="https://doi.org/10.1126/science.ada1615">virulent</a> than BA.1. This means that while BA.2 can spread faster than BA.1, it might not make people sicker.</p>
<p>It is worth noting that while BA.1 has <a href="https://www.who.int/news/item/22-02-2022-statement-on-omicron-sublineage-ba.2">dominated case numbers around the world</a>, it causes <a href="https://www.who.int/news/item/22-02-2022-statement-on-omicron-sublineage-ba.2">less severe disease</a> compared to the delta variant. Recent studies from the <a href="https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1060337/Technical-Briefing-38-11March2022.pdf">U.K.</a> and <a href="https://doi.org/10.2807/1560-7917.ES.2022.27.10.2200181">Denmark</a> suggest that BA.2 may pose a similar risk of hospitalization as BA.1.</p>
<h2>Does previous infection with BA.1 provide protection against BA.2?</h2>
<p>Yes! A <a href="https://doi.org/10.1038/d41586-022-00558-w">recent study</a> suggested that people previously infected with the original BA.1 subvariant have robust protection against BA.2. </p>
<p>Because BA.1 caused widespread infections across the world, it is likely that a significant percentage of the population has protective immunity against BA.2. This is why some scientists predict that BA.2 will be <a href="https://doi.org/10.1038/d41586-022-00471-2">less likely to cause another major wave</a></p>
<p>However, while the <a href="https://doi.org/10.1056/NEJMc2200133">natural immunity</a> gained after COVID-19 infection may provide strong protection against reinfection from earlier variants, it weakens against omicron.</p>
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<figcaption><span class="caption">As long as the SARS-CoV-2 virus continues to infect people, it will have opportunities to produce variants.</span></figcaption>
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<h2>How effective are vaccines against BA.2?</h2>
<p>A <a href="https://doi.org/10.1038/d41586-022-00775-3">recent preliminary study</a> that has not yet been peer reviewed of over 1 million individuals in Qatar suggests that two doses of either the Pfizer–BioNTech or Moderna COVID-19 vaccines protect against symptomatic infection from BA.1 and BA.2 for several months before waning to around 10%. A booster shot, however, was able to elevate protection again close to original levels. </p>
<p>Importantly, both vaccines were 70% to 80% effective at preventing hospitalization or death, and this effectiveness increased to over 90% after a booster dose.</p>
<h2>How worried does the US need to be about BA.2?</h2>
<p>The rise in BA.2 in certain parts of the world is most likely due to a <a href="https://www.npr.org/sections/health-shots/2022/03/19/1087682826/omicron-variant-ba2-surge">combination</a> of its higher transmissibility, people’s waning immunity and relaxation of COVID-19 restrictions. </p>
<p>CDC data suggests that BA.2 cases are rising steadily, making up <a href="https://covid.cdc.gov/covid-data-tracker/#variant-proportions">23% of all cases</a> in the U.S. as of early March. <a href="https://www.npr.org/sections/health-shots/2022/03/19/1087682826/omicron-variant-ba2-surge">Scientists are still debating</a> whether BA.2 will cause another surge in the U.S.</p>
<p>[<em>Climate change, AI, vaccines, black holes and much more.</em> <a href="https://memberservices.theconversation.com/newsletters/?nl=science&source=inline-science-various">Get The Conversation’s best science and health coverage</a>.]</p>
<p>Though there may be an uptick of BA.2 infections in the coming months, <a href="https://theconversation.com/how-long-does-protective-immunity-against-covid-19-last-after-infection-or-vaccination-two-immunologists-explain-177309">protective immunity</a> from vaccination or previous infection provides defense against severe disease. This may make it less likely that BA.2 will cause a significant increase in hospitalization and deaths. The U.S., however, <a href="https://www.nytimes.com/interactive/2022/02/01/science/covid-deaths-united-states.html">lags behind other countries</a> when it comes to vaccination, and falls even further behind on boosters.</p>
<p>Whether there will be another devastating surge depends on how many people are vaccinated or have been previously infected with BA.1. It’s <a href="https://www.cdc.gov/coronavirus/2019-ncov/vaccines/vaccine-benefits.html">safer to generate immunity</a> from a vaccine, however, than from getting an infection. Getting vaccinated and boosted and <a href="https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/prevention.html">taking precautions</a> like wearing an N95 mask and social distancing are the best ways to protect yourself from BA.2 and other variants.</p><img src="https://counter.theconversation.com/content/179619/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Prakash Nagarkatti receives funding from the National Institutes of Health and the National Science Foundation.</span></em></p><p class="fine-print"><em><span>Mitzi Nagarkatti receives funding from NIH.</span></em></p>The latest addition to the omicron lineage has been making waves in Europe. Whether it will do the same in the U.S. depends on rates of vaccination and prior infection.Prakash Nagarkatti, Professor of Pathology, Microbiology and Immunology, University of South CarolinaMitzi Nagarkatti, Professor of Pathology, Microbiology and Immunology, University of South CarolinaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1640732021-08-30T06:06:47Z2021-08-30T06:06:47ZHow long does immunity last after COVID vaccination? Do we need booster shots? 2 immunology experts explain<p>An important factor in achieving <a href="https://www.who.int/news-room/q-a-detail/herd-immunity-lockdowns-and-covid-19">herd immunity</a> against SARS-CoV-2 (the virus that causes COVID-19) is is how long the vaccines protect you. </p>
<p>If a vaccine continues to work well over a long period, it becomes easier to have a significant proportion of the population optimally protected, and in turn suppress or eliminate the disease entirely. </p>
<p>As the rollout of COVID-19 vaccines continues, public attention is increasingly turning to booster shots, which aim to top up immunity if it wanes. But is a third dose needed? And if so, when? </p>
<p>Let’s take a look at what the data tell us so far about how long immunity from COVID-19 vaccines might last.</p>
<h2>First, what about immunity following COVID-19 infection?</h2>
<p>The presence of antibodies against SARS-CoV-2 is used as an indicator of immunity, with higher levels indicating greater protection. Once antibody levels drop below a particular threshold, or vanish completely, the person is at risk of reinfection. </p>
<p>Initially, scientists observed people’s <a href="https://www.nature.com/articles/s41564-020-00813-8">antibody levels rapidly decreased</a> shortly after recovery from COVID-19.</p>
<p>However, more recently, we’ve seen positive signs of long-lasting immunity, with <a href="https://doi.org/10.1038/s41586-021-03647-4">antibody-producing cells</a> in the bone marrow identified seven to eight months following infection with COVID-19. In addition, scientists have observed <a href="https://science.sciencemag.org/content/371/6529/eabf4063">evidence of memory T cells</a> (a type of immune cells) more than six months following infection. </p>
<p>A study of over 9,000 <a href="https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciab345/6251701">recovered COVID-19 patients</a> in the United States up to November 2020 showed a reinfection rate of only 0.7%. These findings closely align with a slightly more <a href="https://www.thelancet.com/journals/eclinm/article/PIIS2589-5370(21)00141-3/fulltext">recent study</a> suggesting reinfection after COVID-19 is very uncommon, at least in the short term. </p>
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<a href="https://theconversation.com/5-ways-our-immune-responses-to-covid-vaccines-are-unique-145248">5 ways our immune responses to COVID vaccines are unique</a>
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<p>While it seems likely there’s some level of lasting protection following COVID-19 infection, if you’ve had COVID, getting vaccinated is still worthwhile.</p>
<p>There’s some evidence vaccination after recovery leads to <a href="https://science.sciencemag.org/content/372/6549/1392">a stronger level of immunity</a> compared to “natural” immunity from infection, or immunity from vaccination alone. People with so-called “hybrid immunity” appear to exhibit a more diverse range of antibodies.</p>
<h2>How long does immunity from vaccines last?</h2>
<p>The vaccines deployed against COVID-19 in Australia and most of the western world come from two classes. </p>
<p>Those produced by <a href="https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)32661-1/fulltext">AstraZeneca</a> and <a href="https://www.nejm.org/doi/full/10.1056/NEJMoa2101544">Johnson & Johnson</a> are viral vector vaccines. They use an adenovirus (which causes the common cold) to prime the immune system to respond to SARS-CoV-2.</p>
<p>The vaccines developed by Pfizer and Moderna use <a href="https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines/mrna.html">mRNA-based technology</a>. The messenger RNA gives your cells temporary instructions to make the coronavirus’ spike protein, teaching your immune system to protect you if you encounter the virus. </p>
<p>For the viral vector vaccines, despite ongoing trials, there’s little data available on the duration of the antibody response. The <a href="https://www.thelancet.com/article/S0140-6736(20)32466-1/fulltext">original studies</a> showed efficacy for <a href="https://jamanetwork.com/journals/jama/fullarticle/2777598">one to two months</a>, however the duration of protection, and whether a booster will be needed, require further evaluation. </p>
<p>Notably, a <a href="https://www.sciencedirect.com/science/article/pii/S1473309920301602">vaccine similar</a> to AstraZeneca against a related coronavirus (Middle East respiratory syndrome, or MERS) showed stable antibody levels over a 12-month follow-up period. This gives hope for lasting protection against similar coronaviruses. </p>
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<a href="https://theconversation.com/how-well-do-covid-vaccines-work-in-the-real-world-162926">How well do COVID vaccines work in the real world?</a>
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<p>The Pfizer and Moderna COVID-19 vaccines are the first vaccines based on mRNA technology to be approved for human use. So there’s still significant research required to evaluate the nature and duration of immunity they induce.</p>
<p>Interestingly, “<a href="https://www.nature.com/articles/s41586-021-03738-2">germinal centers</a>” have been identified in the lymph nodes of people vaccinated with the Pfizer vaccine. These act as training sites for immune cells, teaching them to recognise SARS-CoV-2, indicating a potential for long-lasting protection. </p>
<p>Initial <a href="https://www.nejm.org/doi/full/10.1056/NEJMoa2027906">studies</a> only evaluated short-term efficacy, however recent research has found strong antibody activity at <a href="https://www.nejm.org/doi/full/10.1056/nejmc2103916">six months</a>.</p>
<h2>What about Delta?</h2>
<p>Variants such as Delta, which are <a href="https://theconversation.com/why-is-delta-such-a-worry-its-more-infectious-probably-causes-more-severe-disease-and-challenges-our-vaccines-163579">more transmissible</a> and potentially more dangerous, are likely to increase interest in booster programs. </p>
<p>All vaccines show modestly <a href="https://www.nejm.org/doi/full/10.1056/NEJMoa2108891">reduced efficacy against Delta</a>, so any decrease in protection over time could be more problematic than with the original SARS-CoV-2 virus, or other variants. </p>
<p>A <a href="https://www.ndm.ox.ac.uk/files/coronavirus/covid-19-infection-survey/finalfinalcombinedve20210816.pdf">recent preprint</a> (a study yet to undergo peer review) found protection against the Delta variant waned within three months with both the Pfizer and AstraZeneca vaccines. </p>
<p>This research from the United Kingdom showed the Pfizer vaccine was <a href="https://www.nature.com/articles/d41586-021-02261-8">92% effective</a> at preventing people from developing a high viral load at 14 days after the second dose, but this dropped to 78% at 90 days. AstraZeneca was 69% effective against the same measure at 14 days, dropping to 61% after 90 days.</p>
<p>This study shows vaccinated people who become infected with Delta still carry high amounts of virus (viral load). Third booster doses will be important to reduce these breakthrough infections and subsequent transmission.</p>
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Read more:
<a href="https://theconversation.com/why-do-we-need-booster-shots-and-could-we-mix-and-match-different-covid-vaccines-155951">Why do we need booster shots, and could we mix and match different COVID vaccines?</a>
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<p>Although the UK study looked at infections rather than hospitalisations or deaths, data from <a href="https://theconversation.com/us-is-split-between-the-vaccinated-and-unvaccinated-and-deaths-and-hospitalizations-reflect-this-divide-164460">around the world</a> continue to show the unvaccinated are making up <a href="https://theconversation.com/covid-cases-are-rising-in-highly-vaccinated-israel-but-it-doesnt-mean-australia-should-give-up-and-live-with-the-virus-166404">the vast majority</a> of patients who develop serious illness.</p>
<p>Nonetheless, scientists are continuing to investigate how waning immunity could affect protection against the more serious outcomes of COVID-19.</p>
<h2>OK, so what now?</h2>
<p>Pfizer <a href="https://www.pfizer.com/news/press-release/press-release-detail/pfizer-and-biontech-announce-submission-initial-data-us-fda">has reported positive results</a> from trials of a third dose to boost immunity, and the company <a href="https://www.nbcnews.com/health/health-news/pfizer-seeks-fda-approval-vaccine-booster-dose-n1277634">is seeking</a> formal approval for a booster from the United States Food and Drugs Administration.</p>
<p>The <a href="https://www.cnbc.com/2021/08/18/covid-booster-shots-us-to-begin-wide-distribution-of-third-vaccine-doses-next-month.html">United States</a> has announced it will begin distributing third doses next month to people who received an mRNA vaccine eight months ago or more.</p>
<p>Other countries, such as Israel, have already begun rolling out boosters. The move to offer third doses in some high-income countries has raised <a href="https://theconversation.com/covid-who-calls-for-moratorium-on-booster-shots-is-it-justifiable-165762">ethical concerns</a>, with many people around the world still unable to access a first or second dose.</p>
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<p>A number of countries <a href="https://www.reuters.com/world/europe/french-health-watchdog-backs-covid-vaccine-booster-shot-elderly-vulnerable-2021-08-24/">have authorised</a> booster doses for at-risk populations in response to the rise of the Delta variant. </p>
<p>This includes <a href="https://www.nature.com/articles/d41586-021-02158-6">older adults</a> and those with <a href="https://www.theguardian.com/world/2021/aug/12/fauci-covid-booster-recommended-weakened-immune-systems">compromised immune systems</a>, to combat the increased risk of severe disease and diminished vaccine protection in these people.</p>
<p>In Australia, there is likely to be a booster program in the future. But given the current issues <a href="https://www1.racgp.org.au/newsgp/clinical/focus-on-vaccine-boosters-as-israel-becomes-first">surrounding supply</a>, it’s unlikely to be for some months.</p><img src="https://counter.theconversation.com/content/164073/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Vasso Apostolopoulos COVID-19 research has received internal funding from Victoria University place-based Planetary Health research grant and from philanthropic donations. </span></em></p><p class="fine-print"><em><span>Jack Feehan does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Some countries have started administering third doses of COVID vaccines, or booster shots. But we’re still learning about how long immunity lasts from the first two shots.Vasso Apostolopoulos, Professor of Immunology and Associate Provost, Research Partnerships, Victoria UniversityJack Feehan, Research Officer - Immunology and Translational Research, Victoria UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1505472020-11-30T19:07:47Z2020-11-30T19:07:47ZWhat’s the difference between viral shedding and reinfection with COVID-19?<figure><img src="https://images.theconversation.com/files/371903/original/file-20201130-17-nfmk4h.jpg?ixlib=rb-1.1.0&rect=20%2C0%2C6689%2C4466&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>Over recent weeks and months, we’ve heard of several <a href="https://www.abc.net.au/news/2020-10-21/victoria-covid-cases-viral-shedding-false-positive-explained/12795694">COVID cases</a> in which people have <a href="https://www.adelaidenow.com.au/coronavirus/victorian-woman-moving-to-adelaide-tests-positive-to-covid19-amid-reinfection-fears/news-story/20771f54ea5441690868b2e0f2dd8351">tested positive</a> after previously clearing the virus.</p>
<p>Scientists are hopeful being infected with COVID-19 confers immunity for a length of time. But some of these instances have raised concerns about reinfection. Although rare, it seems to be possible.</p>
<p>The other thing which could be at play in many of these cases is “prolonged viral shedding”.</p>
<p>Both phenomena are probably more common than we realise. But it’s important to understand the differences between the two.</p>
<h2>What is viral shedding?</h2>
<p>When you’re sick with a virus, the cells in your body hosting the infection release infectious virus particles, which you then shed into the environment. This process is called viral shedding.</p>
<p>For <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7461745/">SARS-CoV-2</a>, the virus that causes COVID-19, shedding primarily occurs when we talk, cough, sneeze, or even exhale. SARS-CoV-2 can be shed <a href="https://onlinelibrary.wiley.com/doi/10.1111/apt.16036">in a person’s stool</a>, too.</p>
<p>Research shows shedding of infectious SARS-CoV-2 begins before a person starts displaying symptoms, <a href="https://www.nature.com/articles/s41586-020-2196-x">and peaks</a> at or just after symptom onset (usually four to six days after infection).</p>
<p>Shedding can continue for several weeks after a person’s symptoms have resolved — there’s no standard time frame. </p>
<p>Research has identified shedding of infectious SARS-CoV-2 virus particles <a href="https://www.nature.com/articles/s41586-020-2196-x">from up to eight days</a> after symptom onset in hospitalised patients, to up to <a href="https://www.cell.com/cell/fulltext/S0092-8674(20)31456-2">70 days</a> after diagnosis in an immunocompromised person. </p>
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<img alt="A young woman wrapped in a blanket on the couch looks at a thermometer." src="https://images.theconversation.com/files/371898/original/file-20201130-19-12qd4gj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/371898/original/file-20201130-19-12qd4gj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/371898/original/file-20201130-19-12qd4gj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/371898/original/file-20201130-19-12qd4gj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/371898/original/file-20201130-19-12qd4gj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/371898/original/file-20201130-19-12qd4gj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/371898/original/file-20201130-19-12qd4gj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">People begin shedding SARS-CoV-2 before they develop symptoms.</span>
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<h2>Not all shedding is equal</h2>
<p>In the above cases, the viral particles being shed are infectious, which is what we as virologists consider viral shedding to mean. But during COVID-19, the definition of shedding has been broadened to include the shedding of viral genetic material (RNA).</p>
<p>Although RNA constitutes fragments of the virus, these aren’t necessarily infectious fragments.</p>
<p>Studies measuring the shedding of <a href="https://www.iaea.org/newscenter/news/how-is-the-covid-19-virus-detected-using-real-time-rt-pcr">viral genetic material</a> from the respiratory tract <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7184421/">have reported</a> <a href="https://www.ijidonline.com/article/S1201-9712(20)30352-0/fulltext#%2520">shedding typically lasts</a> around 17 days.</p>
<p>Shedding of SARS-CoV-2 genetic material <a href="https://www.thelancet.com/journals/lanmic/article/PIIS2666-5247(20)30172-5/fulltext">can persist</a> for more than 80 days in the upper respiratory tract, and over 120 days in the stool. </p>
<p>Where people have recovered and then later test positive again — or return a “<a href="https://theconversation.com/why-do-some-covid-19-tests-come-back-with-a-weak-positive-and-why-does-it-matter-147258">weak positive</a>” result — the test has picked up viral genetic material. We don’t know whether the virus is infectious at this point.</p>
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Read more:
<a href="https://theconversation.com/a-man-in-hong-kong-caught-covid-19-a-second-time-heres-why-thats-not-surprising-and-theres-no-need-to-panic-145015">A man in Hong Kong caught COVID-19 a second time. Here's why that's not surprising (and there's no need to panic)</a>
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<h2>So, how can you tell?</h2>
<p>Currently there’s no simple way to determine whether a person is shedding infectious virus, or how much.</p>
<p>The “<a href="https://www.health.gov.au/sites/default/files/documents/2020/11/phln-guidance-on-laboratory-testing-for-sars-cov-2-the-virus-that-causes-covid-19.pdf">gold standard</a>” method used to diagnose COVID-19 is the PCR test. PCR tests detect <a href="https://www.eurosurveillance.org/content/10.2807/1560-7917.ES.2020.25.3.2000045">viral genetic material</a> (RNA in the case of SARS-CoV-2) from a patient’s swabbed samples.</p>
<p>But they can’t determine whether the virus is alive or dead, or, in other words, <a href="https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/926410/Understanding_Cycle_Threshold__Ct__in_SARS-CoV-2_RT-PCR_.pdf">if the virus is infectious</a>.</p>
<p>The level of infectious SARS-CoV-2 can only be determined using <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7293183/">infectivity methods</a> (called <a href="https://www.youtube.com/watch?v=tGVDYGxqtJ0">assays</a>). These are common in research laboratories, but are not used as diagnostic tests. </p>
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Read more:
<a href="https://theconversation.com/how-long-are-you-infectious-when-you-have-coronavirus-135295">How long are you infectious when you have coronavirus?</a>
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<h2>Why do some people shed for longer?</h2>
<p>There’s <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7455175/">no evidence</a> to suggest people who shed SARS-CoV-2 genetic material for a long time in their faeces have been sicker with COVID-19. Though <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7190077/">some research</a> has found prolonged shedding in the respiratory tract can be linked to more severe disease.</p>
<p>We don’t fully understand the factors that make a person a “long shedder”, but research into this is ongoing. Certain groups have been <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7184421/">associated with</a> prolonged SARS-CoV-2 shedding, including males, <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7141453/">children</a>, older adults, and people with compromised immune systems.</p>
<p>There’s also speculation factors such as the amount of SARS-CoV-2 which caused the infection (the viral dose), and possibly the <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7174922/">viral strain</a>, may play a role.</p>
<p>In the absence of targeted <a href="https://www.tandfonline.com/doi/full/10.1080/17476348.2021.1854092">antiviral drugs</a>, shedding can’t be stopped. But, by sticking to COVID-safe guidelines such as keeping an adequate distance from others, wearing a face mask, and practising hand hygiene, we can minimise the risks from a person unknowingly shedding infectious virus.</p>
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<img alt="A man washing his hands with soap." src="https://images.theconversation.com/files/371900/original/file-20201130-22-13hylvg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/371900/original/file-20201130-22-13hylvg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/371900/original/file-20201130-22-13hylvg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/371900/original/file-20201130-22-13hylvg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/371900/original/file-20201130-22-13hylvg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/371900/original/file-20201130-22-13hylvg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/371900/original/file-20201130-22-13hylvg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Following COVID-safe measures can protect against viral shedding.</span>
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<h2>Long viral shedding versus reinfection</h2>
<p>Reports of reinfection — in the sense of a new infection, rather than prolonged or intermittent shedding of the same one — <a href="https://doi.org/10.1016/S1473-3099(20)30783-0">have been limited</a> to date. One source collating confirmed reinfection cases <a href="https://bnonews.com/index.php/2020/08/covid-19-reinfection-tracker/">indicates</a> there have been just 26 worldwide.</p>
<p>Evidence we have from other coronaviruses suggests the risk of reinfection may be lower in <a href="https://www.cdc.gov/coronavirus/2019-ncov/hcp/duration-isolation.html">the first 90 days</a> after initial infection. </p>
<p>Some studies on COVID-19, both <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7533664/">published</a> and <a href="https://www.biorxiv.org/content/10.1101/2020.11.15.383323v1">not yet formally published in a peer-reviewed journal</a>, suggest immunity may last for several months. But we need more evidence on this topic, which we will accumulate as time passes.</p>
<p>Where a person does test positive several weeks or months after they’ve recovered, <a href="https://www.usatoday.com/story/news/health/2020/11/13/covid-19-reinfection-vaccines-herd-immunity-health/6136943002/">the difficulty is confirming reinfection</a>. That’s because this requires genetic testing of both infections to determine whether they are in fact different. </p>
<p>Given this is time consuming and the technology isn’t widely accessible, it’s highly likely there are more than 26 cases of reinfection around the world.</p>
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<a href="https://theconversation.com/new-research-suggests-immunity-to-covid-is-better-than-we-first-thought-150645">New research suggests immunity to COVID is better than we first thought</a>
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<h2>Shedding, reinfection and community spread</h2>
<p>While the virus appears to be under good control in Australia, prolonged viral shedding and reinfection are probably two of the most important drivers of SARS-CoV-2 community transmission around the world.</p>
<p>Understanding how and for how long people can shed SARS-CoV-2, and which factors increase the risk of viral shedding or reinfection, can help us to improve surveillance and reduce the rate at which the virus spreads.</p><img src="https://counter.theconversation.com/content/150547/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>It’s not only shedding and reinfection which are different — there are actually two types of viral shedding.Lara Herrero, Research Leader in Virology and Infectious Disease, Griffith UniversityEugene Madzokere, PhD Candidate in Virology, Griffith UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1479602020-10-16T12:12:57Z2020-10-16T12:12:57ZCoronavirus reinfection cases: what we know so far – and the vital missing clues<p>As President Trump claims that he is <a href="https://www.independent.co.uk/news/world/americas/us-politics/trump-coronavirus-covid-immune-fox-interview-protective-glow-b964840.html">immune to COVID-19</a> and isolated reports emerge of reinfection, what is the truth about immunity to COVID-19?</p>
<p>To date, there have been <a href="https://sindmepa.org.br/wp-content/uploads/2020/08/COVID-19-re-infection-by-a-phylogenetically-distinct-SARS-coronavirus-2-strain.pdf">six</a> <a href="https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(20)30764-7/fulltext">published</a> <a href="https://www.unboundmedicine.com/medline/citation/32887979/Symptomatic_SARS-CoV-2_reinfection_by_a_phylogenetically_distinct_strain.">cases</a> of COVID-19 reinfection, with various other unverified accounts from around the world. Although this is a comparably small fraction of <a href="https://www.worldometers.info/coronavirus/">the millions of people</a> known to have been infected, should we be concerned? To unpick this puzzle, we must first consider what we mean by immunity.</p>
<h2>How immunity works</h2>
<p>When we are infected with any pathogen, our immune system quickly responds to try to contain the threat and minimise any damage. Our first line of defence is from immune cells, known as innate cells. These cells are not usually enough to eliminate a threat, which is where having a more flexible “adaptive” immune response comes into play – our lymphocytes.</p>
<p>Lymphocytes come in two main varieties: B lymphocytes, which make antibodies, and T lymphocytes, which include cells that directly kill the germy invaders. </p>
<p>As antibodies are readily measured in blood, they are often used to indicate a good adaptive immune response. However, over time, antibodies levels in our blood wane, but this doesn’t necessarily mean protection is lost. We retain some lymphocytes that know how to deal with the threat – our memory cells. Memory cells are remarkably long-lived, patrolling our body, ready to spring into action when needed. </p>
<p>Vaccines work by creating memory cells without the risk of a potentially fatal infection. In an ideal world, it would be relatively easy to create immunity, but it’s not always that straightforward.</p>
<p>Although our immune system has evolved to deal with a huge variety of pathogens, these germs have also evolved to hide from the immune system. This arms race means that some pathogens such as malaria or HIV are very tricky to deal with. </p>
<p>Infections that have spilled over from animals – zoonotic diseases – are also challenging for our immune system because they can be completely novel. The virus that causes COVID-19 is such a zoonotic disease, originating in <a href="https://www.nature.com/articles/s41467-020-17687-3">bats</a>.</p>
<p>COVID-19 is caused by a betacoronavirus. Several betacoronaviruses are already common in the human population – most familiar as a cause of the common cold. Immunity to these cold-causing viruses isn’t that <a href="https://www.nature.com/articles/s41467-020-18450-4">robust</a> but immunity to the more serious conditions, Mers and <a href="https://www.nature.com/articles/s41467-020-18450-4">Sars</a>, is more durable. </p>
<p>Data to date on COVID-19 shows that antibodies can be detected three months after infection, although, as with Sars and Mers, antibodies gradually decrease <a href="https://immunology.sciencemag.org/content/5/52/eabe5511">over time</a>. </p>
<p>Of course, antibody levels are not the only indication of immunity and don’t tell us about T lymphocytes or our memory cells. The virus causing COVID-19 is structurally similar to <a href="https://www.sciencedirect.com/science/article/pii/S0092867420302622">Sars</a>, so perhaps we can be more optimistic about a more durable protective response – time will tell. So how worried then should we be about reports of reinfection with COVID-19?</p>
<h2>How worried should we be?</h2>
<p>The handful of case reports on reinfection with COVID-19 don’t necessarily mean that immunity is not occurring. Issues with testing could account for some reports because “virus” can be detected after infection and <a href="https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)31483-5/fulltext">recovery</a>. The tests look for viral RNA (the virus’s genetic material), and viral RNA that cannot cause infection can be shed from the body even after the person has recovered. </p>
<p>Conversely, false-negative results happen when the sample used in testing contains insufficient viral material to be detected – for example, because the virus is at a very low level in the body. Such apparent negative results may account for cases in which the interval between the first and second infection is short. It is hugely important, therefore, to use additional measures, such as viral sequencing and immune indicators. </p>
<p>Reinfection, even in immunity, can happen, but usually this would be mild or asymptomatic because the immune response protects against the worst effects. Consistent with this is that most verified cases of reinfection reported either no or mild symptoms. However, one of the latest verified cases of reinfection – which happened just 48 days after the initial infection – actually had a more severe response to <a href="https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(20)30764-7/fulltext">reinfection</a>.</p>
<p>What might account for the worse symptoms the second time round? One possibility is the patient did not mount a robust adaptive immune response first time round and that their initial infection was largely contained by the innate immune response (the first line of defence). One way to monitor this would be to assess the antibody response as the type of antibody detected can tell us something about the timing of infection. But unfortunately, antibody results were not analysed in the recent patient’s first infection. </p>
<p>Another explanation is that different viral strains caused the infections with a subsequent impact on immunity. Genetic sequencing did show differences in viral strains, but it isn’t known if this equated to altered immune recognition. Many viruses share structural features, enabling immune responses to one virus to protect against a similar virus. This has been suggested to account for the lack of symptoms in young children who frequently get colds caused by betacoronaviruses. </p>
<p>However, a <a href="https://www.medrxiv.org/content/10.1101/2020.10.08.20209650v1">recent study</a>, yet to be peer-reviewed, found that protection against cold-causing coronaviruses did not protect against COVID-19. In fact, antibodies recognising similar viruses can be dangerous – accounting for the rare phenomenon of antibody-dependent enhancement of disease (ADE). ADE occurs when antibodies enhance viral infection of cells with potentially life-threatening consequences. </p>
<p>It should be emphasised, though, that antibodies are only one indicator of immunity and we have no data on either T lymphocytes or memory cells in these cases. What these cases emphasise is a need to standardised approaches in order to capture the critical information for robust evaluation of the threat of reinfection.</p>
<p>We are still learning about the immune response to COVID-19, and every piece of new data is helping us unpick the puzzle of this challenging virus. Our immune system is a powerful ally in the fight against infection, and only by unlocking it can we ultimately hope to defeat COVID-19.</p><img src="https://counter.theconversation.com/content/147960/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sheena Cruickshank does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Reports of reinfection shouldn’t be cause for alarm. If we gather the right data, they can teach us a lot about the immune response.Sheena Cruickshank, Professor in Biomedical Sciences, University of ManchesterLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1454762020-09-14T11:47:40Z2020-09-14T11:47:40ZWhy a vaccine can provide better immunity than an actual infection<p>Two recent studies have confirmed that people previously infected with SARS-CoV-2, the virus that causes COVID-19, can be reinfected with the virus. Interestingly, the two people had different outcomes. The <a href="https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciaa1275/5897019">person in Hong Kong</a> showed no symptoms on the second infection, while the case from <a href="https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3680955">Reno, Nevada,</a> had more severe disease the second time around. It is therefore unclear if an immune response to SARS-CoV-2 will protect against subsequent reinfection. </p>
<p>Does this mean a vaccine will also fail to protect against the virus? Certainly not. First, it is still unclear how common these reinfections are. More importantly, a fading immune response to natural infection, as seen in the Nevada patient, does not mean we cannot develop a successful, protective vaccine. </p>
<p>Any infection initially activates a non-specific innate immune response, in which white blood cells trigger inflammation. This may be enough to clear the virus. But in more prolonged infections, the adaptive immune system is activated. Here, T and B cells recognise distinct structures (or antigens) derived from the virus. T cells can detect and kill infected cells, while B cells produce antibodies that neutralise the virus. </p>
<p>During a primary infection – that is, the first time a person is infected with a particular virus – this adaptive immune response is delayed. It takes a few days before immune cells that recognise the specific pathogen are activated and expanded to control the infection. </p>
<p>Some of these T and B cells, called memory cells, persist long after the infection is resolved. It is these memory cells that are crucial for long-term protection. In a subsequent infection by the same virus, the memory cells get activated rapidly and induce a robust and specific response to block the infection. </p>
<p>A vaccine mimics this primary infection, providing antigens that prime the adaptive immune system and generating memory cells that can be activated rapidly in the event of a real infection. However, as the antigens in the vaccine are derived from weakened or noninfectious material from the virus, there is little risk of severe infection. </p>
<h2>A better immune response</h2>
<p>Vaccines have other advantages over natural infections. For one, they can be designed to focus the immune system against specific antigens that elicit better responses. </p>
<p>For instance, the <a href="https://translational-medicine.biomedcentral.com/articles/10.1186/1479-5876-8-105">human papillomavirus (HPV) vaccine</a> elicits a stronger immune response than infection by the virus itself. One reason for this is that the vaccine contains high concentrations of a viral coat protein, more than what would occur in a natural infection. This triggers strongly neutralising antibodies, making the vaccine very effective at preventing infection. </p>
<p>The natural immunity against HPV is especially weak, as the virus uses various tactics to evade the host immune system. Many viruses, including HPV, have proteins that block the immune response or simply lie low to avoid detection. Indeed, a vaccine that provides accessible antigens in the absence of these other proteins may allow us to control the response in a way that a natural infection does not. </p>
<p>The immunogenicity of a vaccine – that is, how effective it is at producing an immune response – can also be fine tuned. Agents called adjuvants typically kick-start the immune response and can enhance vaccine immunogenicity. </p>
<p>Alongside this, the dose and route of administration can be controlled to encourage appropriate immune responses in the right places. Traditionally, vaccines are administered by injection into the muscle, even for respiratory viruses such as measles. In this case, the vaccine generates such a strong response that antibodies and immune cells reach the mucosal surfaces in the nose. </p>
<p>However, the <a href="https://www.sciencedirect.com/science/article/pii/S0952791512000635#bib0015">success of the oral polio vaccine</a> in reducing infection and transmission of polio has been attributed to a localised immune response in the gut, where poliovirus replicates. Similarly, delivering the coronavirus vaccine directly to the nose may contribute to a stronger <a href="https://www.tandfonline.com/doi/full/10.1080/14712598.2020.1767062">mucosal</a> <a href="https://www.sciencedirect.com/science/article/pii/S0092867420310680">immunity</a> in the nose and lungs, offering protection at the site of entry.</p>
<h2>Understanding natural immunity is key</h2>
<p>A good vaccine that improves upon natural immunity requires us to first understand our natural immune response to the virus. So far, neutralising antibodies against SARS-CoV-2 have been <a href="https://www.nejm.org/doi/full/10.1056/NEJMoa2026116">detected</a> up to four months after infection. </p>
<p><a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2271881/">Previous</a> <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2851497/">studies</a> have suggested that antibodies against related coronaviruses typically last for a couple of years. However, declining antibody levels do not always translate to weakening immune responses. And more promisingly, a recent <a href="https://www.nature.com/articles/s41586-020-2550-z">study</a> found that memory T cells triggered responses against the coronavirus that causes Sars almost two decades after the people were infected. </p>
<p>Of the roughly <a href="https://www.nature.com/articles/d41573-020-00151-8">320 vaccines</a> being developed against COVID-19, one that favours a strong T cell response may be the key to long-lasting immunity.</p><img src="https://counter.theconversation.com/content/145476/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Maitreyi Shivkumar does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>A few people have developed COVID-19 twice. That doesn’t mean a vaccine can’t offer long-term protection.Maitreyi Shivkumar, Senior Lecturer in Molecular Biology, De Montfort UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1450152020-08-26T02:33:30Z2020-08-26T02:33:30ZA man in Hong Kong caught COVID-19 a second time. Here’s why that’s not surprising (and there’s no need to panic)<p>A Hong Kong man who recovered from COVID-19 more than four months ago has reportedly been reinfected with SARS-CoV-2, the virus that causes COVID-19. This time he didn’t have any symptoms.</p>
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<p>This is not necessarily unexpected, because very few natural infections generate an immune response that completely prevents reinfection. Instead, what generally happens after an infection is that the body’s immune response gradually declines over months after the infection is cleared. </p>
<p>Specialised immune cells in the body are tasked with remembering each particular infection, so if you get infected again your body quickly starts producing the relevant antibodies and other immune cells (called T cells) in large numbers. This helps clear the new infection more rapidly and effectively. So you can still get reinfected, but you’re more likely to have fewer symptoms or be asymptomatic.</p>
<p>This is what seems to have happened to the 33-year-old Hong Kong man at the centre of the latest reports. The first infection caused symptoms, which he reportedly suffered from for some time. But the second time around he was asymptomatic, presumably because his body effectively repelled the disease. </p>
<p>The same phenomenon has previously been shown in monkeys, with one experimental study showing reinfection with SARS-CoV-2 is possible, but that <a href="https://www.biorxiv.org/content/10.1101/2020.03.13.990226v1">reinfection did not result in the development of disease</a>.</p>
<p>However, we have to be careful about over-interpreting what we know about this case. This is just one person. Is he the exception or the rule? We don’t know yet for sure, and we have to wait for further research. Also, his case was announced via a <a href="https://twitter.com/cwylilian/status/1297830744509698050">press release</a>, so we have to wait for the paper to be officially published to be able to properly scrutinise the data. </p>
<h2>A different strain</h2>
<p>There have been anecdotal reports of people being reinfected before, but many of these seem to be cases in which the initial infection simply persisted for a long time, or in which the person’s lungs were <a href="https://www.sciencealert.com/those-positive-results-from-recovered-covid-19-patients-weren-t-reinfections-after-all">expelling dead virus</a>.</p>
<p>But in this case, the virus isolated from the man’s two separate positive COVID-19 tests had slightly different genetic sequences. This suggests they had a different origin and are therefore different strains.</p>
<p>So far, there have been many SARS-CoV-2 mutations <a href="https://www.sciencedirect.com/science/article/pii/S1567134820300915?via%3Dihub">detected</a> around the world. One particular mutant strain, known as the G-variant, seems to be <a href="https://www.sciencedirect.com/science/article/pii/S0092867420308205">more infectious than the original virus</a>.</p>
<p>We must remember, however, it’s common for viruses to mutate. So it’s also possible we’ll need several different vaccines to account for multiple strains of the virus, like is often done with the flu vaccine.</p>
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Read more:
<a href="https://theconversation.com/the-oxford-deal-is-welcome-but-remember-the-vaccine-hasnt-been-proven-to-work-yet-144726">The Oxford deal is welcome, but remember the vaccine hasn't been proven to work yet</a>
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<h2>What does this mean for our immune system?</h2>
<p>The good news is this particular person’s immune system seems to have recognised the second infection, as shown by the fact his blood boosted antibodies against it. Despite the mutation, the man could still mount a good defence against the new strain. </p>
<p>Antibodies usually last in the <a href="https://www.ncbi.nlm.nih.gov/books/NBK27158/">blood for roughly 120 days</a> following a stimulus such as natural infection with a virus or injection with a vaccine, though it varies depending on the disease. Both the B cells that produce antibodies, and the T cells that kill infected cells, also wane over time after the stimulus.</p>
<p>Vaccines can induce longer-lasting responses. But the key point is both natural infections and vaccines do generate memory B and T cells. So when the body comes in contact with the infection the second time, the memory cells respond rapidly and in high numbers. This can be so quick and strong that in some cases it can even result in “<a href="https://www.sciencedirect.com/science/article/pii/S1876034120305670">sterile protection</a>”, effectively preventing the virus from infecting our cells. More commonly, there may be a small lag time for the immune system to respond fully, but in the end the virus is still unlikely to infect many cells.</p>
<h2>He didn’t develop symptoms, but could he still pass it on?</h2>
<p>At the moment it’s unclear if asymptomatic carriers can transmit infection. Indeed, there may be <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7228388/">different types of asymptomatic carriers</a>. Some asymptomatic people might transmit the virus, while others don’t. We don’t know why this is the case.</p>
<p>But based on our experience with other diseases, the higher the number of viral particles being spread from person to person, the higher the chance of infection. Therefore, asymptomatic carriers, who do not shed lots of virus through coughing or sneezing, should in theory have a lower risk of infecting others.</p>
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Read more:
<a href="https://theconversation.com/exposure-to-common-colds-might-give-some-people-a-head-start-in-fighting-covid-19-143455">Exposure to common colds might give some people a head start in fighting COVID-19</a>
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<h2>Does reinfection mean herd immunity is impossible?</h2>
<p>Herd immunity is still possible if we get a successful vaccine, because vaccines can be more powerful and protective than the immunity conferred by being naturally infected with the virus. Some epidemiologists suggest <a href="https://www.jhsph.edu/covid-19/articles/achieving-herd-immunity-with-covid19.html">at least 70%</a> of a population needs to be immunised to achieve herd immunity. </p>
<p>What’s more, becoming reinfected does not mean the virus will necessarily be transmitted — it depends on the viral dose and the susceptibility of people around the infected person. If they are all immunised with a vaccine, we generate a ring of fire that can contain spread of the virus.</p>
<p>It’s also possible SARS-CoV-2 becomes an endemic virus, like many viruses circulating in the population. But as long as there are diagnostics, vaccines and treatments, we could continue functioning normally just as we do with influenza present in the population. Ultimately it’s about what level of risk society is willing to accept. And we may need to use infection control methods like masks and hand hygiene for some time.</p>
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Read more:
<a href="https://theconversation.com/no-australia-should-not-follow-swedens-approach-to-coronavirus-143540">No, Australia should not follow Sweden's approach to coronavirus</a>
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<img src="https://counter.theconversation.com/content/145015/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>This is just one person. Is he the exception? Is he the rule? We don’t know yet for sure. But reinfection is definitely possible.Vasso Apostolopoulos, Professor of Immunology and Pro Vice-Chancellor, Research Partnerships, Victoria UniversityMagdalena Plebanski, Professor of Immunology, RMIT UniversityMaja Husaric, Lecturer; MD, Victoria UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1449652020-08-25T15:25:25Z2020-08-25T15:25:25ZCoronavirus reinfection – what it actually means, and why you shouldn’t panic<p>Scientists in Hong Kong have reported the <a href="https://twitter.com/cwylilian/status/1297857565385093121">first confirmed case</a> of reinfection with the coronavirus that causes COVID-19, reportedly backed up by genetic sequences of the two episodes of the 33-year-old man’s infections in March and in August 2020. Naturally people are worried what this could mean for our chances of resolving the pandemic. Here’s why they shouldn’t worry. </p>
<p>Nearly nine months after the first infection with the novel coronavirus, we have very poor evidence for reinfection. However, virologists understand that reinfection with <a href="https://www.cdc.gov/coronavirus/general-information.html#:%7E:text=Common%20human%20coronaviruses%2C%20including%20types,some%20point%20in%20their%20lives.">coronaviruses</a> is common, and immunologists are working hard to determine how long the hallmarks of protective immunity will last in recovered patients. </p>
<p>The rare reports of reinfection so far were not accompanied by virus sequencing data so they could not be confirmed, but they are quite expected and there is no cause for alarm. </p>
<h2>Inhospitable hosts</h2>
<p>Our bodies do not become impervious to viruses when we recover from infection, instead, in many cases, they become inhospitable hosts. Consider that beyond recovery, our bodies often still offer the same cell types – such as cells of the respiratory tract – that viruses latch onto and gain entry for a cosy haven to uncoat and begin producing more viruses. These target cells are not altered in any substantial way to prevent future infections months after the virus has been cleared by the immune response.</p>
<p>If antibodies and memory cells (B and T cells) are left behind from a recent infection, however, the new expansion of the virus is rather short lived and the infection is subdued before the host suffers too much – or even notices at all. </p>
<p><a href="https://twitter.com/VirusesImmunity/status/1297890418168860674">This</a> appears to be the case with the Hong Kong patient, who did not present any symptoms of the second infection, which was discovered following routine testing at the airport. Would he ever know that he had been reinfected had he not travelled? Probably not. A more interesting question is, was he contagious during his asymptomatic second infection? </p>
<p>There is mounting evidence that asymptomatic and presymptomatic people are contagious and this is why the sensible official advice is to wear face coverings to avoid infecting other people and to keep our distance to avoid getting infected. Coronaviruses from previous colds have endowed some of us with <a href="https://www.nature.com/articles/s41586-020-2550-z">memory T cells</a> that can also mobilise against the novel coronavirus, and this could explain why some people are spared severe disease.</p>
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<img alt="Woman putting a face mask on" src="https://images.theconversation.com/files/354670/original/file-20200825-24-udnubv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/354670/original/file-20200825-24-udnubv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/354670/original/file-20200825-24-udnubv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/354670/original/file-20200825-24-udnubv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/354670/original/file-20200825-24-udnubv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=425&fit=crop&dpr=1 754w, https://images.theconversation.com/files/354670/original/file-20200825-24-udnubv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=425&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/354670/original/file-20200825-24-udnubv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=425&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Even if you’ve recovered from an infection, you should still follow official advice, such as wearing a mask.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/woman-wearing-anti-virus-protection-mask-1678274461">r.classen/Shutterstock</a></span>
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<h2>Three potential outcomes</h2>
<p>So how should we receive the news on reinfection of recovered individuals? There are three possible outcomes of reinfection with a similar virus: worse symptoms that lead to more severe disease, the same symptoms as the first infection, and improvement of symptoms leading to milder or no disease. </p>
<p>The first outcome is known as disease enhancement and is noted in patients infected with similar strains of viruses such as <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5858873/">dengue</a>. There is no evidence for this for the novel coronavirus, despite over 23 million confirmed cases of COVID-19 worldwide. </p>
<p>The second outcome, where the patient suffers the same disease twice, indicates that there is no sufficient immunological memory left behind to protect from reinfection. This could happen if the first infection did not require antibodies or T cells to be resolved, perhaps because other <a href="https://www.ncbi.nlm.nih.gov/books/NBK26846/">rapidly deployed immune defences</a> were enough to control it. </p>
<p>The final outcome is milder infection thanks to a healthy immune system that generated antibodies and memory B and T cell responses that persisted long enough to be of value during the second exposure. Given the <a href="https://immunology.sciencemag.org/content/5/48/eabd2071">diversity</a> of antibody and T cell responses reported in different COVID-19 patients, we anticipate that immune protection – if efficient – may vary in different people. </p>
<p>Of course, this has implications for the potency and duration of herd immunity, the idea that when we reach a large number of recovered patients immune to reinfection, this will protect the most vulnerable. Therefore vaccination is critical to induce and sustain protective immune responses in the long term. </p>
<p>Vaccination can elicit more potent and longer-lasting immune responses compared with natural infection, and these can be sustained by booster vaccinations when necessary. This is why scientists were not surprised to hear of evidence of reinfection. The lack of symptoms experienced by the Hong Kong patient is very good news.</p><img src="https://counter.theconversation.com/content/144965/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Zania Stamataki is a viral immunologist at the University of Birmingham, UK. She is a member of the British Society for Immunology and she cultures SARS-CoV-2 in category 3 containment labs to characterise immune responses to the virus and to support the development of disinfectants and antivirals. </span></em></p>Scientists were not surprised by reports on coronavirus reinfection; the lack of symptoms on reinfection is encouraging.Zania Stamataki, Senior Lecturer in Viral Immunology, University of BirminghamLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1449912020-08-25T12:24:42Z2020-08-25T12:24:42ZA man was reinfected with coronavirus after recovery – what does this mean for immunity?<figure><img src="https://images.theconversation.com/files/354454/original/file-20200824-22-kbunl3.jpg?ixlib=rb-1.1.0&rect=14%2C36%2C4808%2C3176&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Is it possible to get COVID-19 twice?</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/man-wearing-a-face-mask-as-a-precautionary-measure-against-news-photo/1228166500?adppopup=true">May James/AFP via Getty Images</a></span></figcaption></figure><p>A 33-year old man was found to have <a href="https://www.statnews.com/2020/08/24/first-covid-19-reinfection-documented-in-hong-kong-researchers-say/">a second SARS-CoV-2 infection</a> some four-and-a-half months after he was diagnosed with his first, from which he recovered. The man, who showed no symptoms, was diagnosed when he returned to Hong Kong after a trip to Spain. </p>
<p><a href="https://scholar.google.com/citations?user=ubfhdQwAAAAJ&hl=en">I am a virologist</a> with expertise in coronaviruses and enteroviruses, and I’ve been curious about reinfections since the beginning of the pandemic. Because people infected with SARS-CoV-2 can often test positive for the virus for weeks to months, likely due to the sensitivity of the test and <a href="https://doi.org/10.1002/jmv.25952">leftover RNA fragments</a>, the only way to really answer the question of reinfection is by sequencing the viral genome at the time of each infection and looking for differences in the genetic code. </p>
<p>There is no published peer-review report on this man – only a press release from the University of Hong Kong – although reports say the work will be published in the journal <a href="https://academic.oup.com/cid">Clinical Infectious Diseases</a>. Here I address some questions raised by the current news reports. </p>
<h2>Why wasn’t the man immune to reinfection?</h2>
<p>Immunity to endemic coronaviruses – those that cause symptoms of the common cold – <a href="http://doi.org/10.1136/adc.58.7.500">is relatively short-lived</a>, <a href="http://doi.org/10.1017/s0950268800048019">with reinfections occurring</a> even within the same season. So it isn’t completely surprising that reinfection with SARS-CoV-2, the virus that causes COVID-19, might be possible.</p>
<p><a href="https://www.ncbi.nlm.nih.gov/books/NBK279396/">Immunity is complex and involves multiple mechanisms</a> in the body. That includes the generation of antibodies – through what’s known as the adaptive immune response – and through the actions of T-cells, which can help to educate the immune system and to specifically eliminate virus-infected cells. However, researchers around the world are still learning about immunity to this virus and so can’t say for sure, based on this one case, whether reinfection will be a cause for broad concern.</p>
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<h2>How different is the second strain that infected the Hong Kong man?</h2>
<p>“Strain” has a particular definition when referring to viruses. Often a different “strain” is a virus that behaves differently in some way. The coronavirus that infected this man in Europe is likely not a new strain. </p>
<p>A <a href="https://www.statnews.com/2020/08/24/first-covid-19-reinfection-documented-in-hong-kong-researchers-say/">STAT News article</a> reports that the <a href="https://nextstrain.org/ncov/global">genetic make up of the sequenced virus</a> from the patient’s second infection had 24 nucleotides – building blocks of the virus’s RNA genome – that differed from the <a href="https://www.ncbi.nlm.nih.gov/nuccore/1798174254">SARS-CoV-2 isolate</a> that infected him the first time. </p>
<p>SARS-CoV-2 has a genome that is made up of about 30,000 nucleotides, so the virus from the man’s second infection was roughly 0.08% different than the original in genome sequence. That shows that the virus that caused the second infection was new; not a recurrence of the first virus. </p>
<h2>The man was asymptomatic – what does that mean?</h2>
<p>The man wasn’t suffering any of the hallmark COVID-19 symptoms which might mean he had some degree of protective immunity to the second infection because he didn’t seem sick. But this is difficult to prove.</p>
<p>I see three possible explanations. The first is that the immunity he gained from the first infection protected him and allowed for a mild second infection. Another possibility is that the infection was mild because he was presymptomatic, and went on to develop symptoms in the coming days. Finally, sometimes infections with SARS-CoV-2 are asymptomatic – at the moment it is difficult to determine whether this was due to the differences in the virus or in the host.</p>
<h2>What can we say about reinfection based on this one case?</h2>
<p>Only that it seems to be possible after enough time has elapsed. We do not know how likely or often it is to occur.</p>
<h2>Should people who have recovered from COVID-19 still wear a mask?</h2>
<p>As we are still learning about how humans develop immunity to SARS-CoV-2 after infection, my recommendation is for continued masking, hand hygiene and distancing practices, even after recovery from COVID-19, to protect against the potential for reinfection.</p><img src="https://counter.theconversation.com/content/144991/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Megan Culler Freeman is funded by the Pediatric Infectious Diseases Society St. Jude Children's Research Hospital Fellowship in Basic and Translational Research. </span></em></p>Reports describe a Hong Kong man who was reinfected with the coronavirus after returning from Europe. Does that mean he wasn’t immune after the first infection?Megan Culler Freeman, Pediatric Infectious Diseases Fellow, University of PittsburghLicensed as Creative Commons – attribution, no derivatives.