tag:theconversation.com,2011:/africa/topics/vaccine-immunity-101974/articlesVaccine immunity – The Conversation2021-12-09T13:34:54Ztag:theconversation.com,2011:article/1733962021-12-09T13:34:54Z2021-12-09T13:34:54ZFiguring out omicron – here’s what scientists are doing right now to understand the new coronavirus variant<figure><img src="https://images.theconversation.com/files/436465/original/file-20211208-137612-ikwh0c.jpg?ixlib=rb-1.1.0&rect=686%2C0%2C7210%2C5150&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A researcher works with COVID-19 samples from patients.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/laboratory-operator-handles-positive-covid-19-samples-to-be-news-photo/1237075524">Thomas Samson/AFP via Getty Images</a></span></figcaption></figure><p><em>Scientists around the world have been racing to learn more about the new omicron strain of SARS-CoV-2, first declared a <a href="https://www.who.int/news/item/26-11-2021-classification-of-omicron-(b.1.1.529)-sars-cov-2-variant-of-concern">“variant of concern” on Nov. 26, 2021</a> by the World Health Organization. Officials cautioned that it would take several weeks before they’d know whether the recently emerged coronavirus variant is more contagious and causes more or less serious COVID-19 than delta and other earlier variants, and whether current vaccines can ward it off.</em></p>
<p><em><a href="https://scholar.google.com/citations?user=OQ7vzu0AAAAJ&hl=en&oi=ao">Peter Kasson is a virologist and biophysicist</a> at the University of Virginia who studies how viruses such as SARS-CoV-2 enter cells and what can be done to stop them. Here he explains what lab-based scientists are doing to help answer the outstanding questions about omicron.</em></p>
<h2>Does prior immunity protect against omicron?</h2>
<p>These are the key lab results everyone is waiting for: How effective are the antibodies people already have at fighting off omicron? If you got the booster shot, are you protected? Or if you had COVID-19 and then were vaccinated?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/436467/original/file-20211208-25-152atd7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="artist's rendition of a virus with antibodies surrounding it" src="https://images.theconversation.com/files/436467/original/file-20211208-25-152atd7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/436467/original/file-20211208-25-152atd7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/436467/original/file-20211208-25-152atd7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/436467/original/file-20211208-25-152atd7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/436467/original/file-20211208-25-152atd7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/436467/original/file-20211208-25-152atd7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/436467/original/file-20211208-25-152atd7.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"></a>
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<span class="caption">Will the antibodies people already have recognize and thwart omicron?</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/antibodies-attacking-sars-cov-2-virus-corona-virus-royalty-free-image/1328466445">Dr_Microbe/iStock via Getty Images</a></span>
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<p>The goal is to see how well antibodies from real people who have had COVID-19 or have been vaccinated against it can hold off omicron in petri dishes in the lab. Scientists expect that antibodies from people exposed to other variants won’t work as well against omicron because of its mutations, but they need to measure how much less well and whether it’s still enough to stop the virus. </p>
<p>To answer these questions, most researchers first make a version of the SARS-CoV-2 virus that can <a href="https://doi.org/10.3390/v12050513">enter cells but not reproduce</a>. A few specialized labs with <a href="https://theconversation.com/we-work-with-dangerous-pathogens-in-a-downtown-boston-biocontainment-lab-heres-why-you-can-feel-safe-about-our-research-163197">extra levels of biosecurity</a> use the actual virus. Scientists add antibodies from the blood of people vaccinated against or recovered from COVID-19 to the virus. They then mix this with human lung cells to see whether the antibodies can stop the virus from infecting the cells.</p>
<p>My laboratory performs this kind of work with <a href="https://doi.org/10.1038/s41541-021-00399-0">SARS-CoV-2</a> and other <a href="https://doi.org/10.1021/acscentsci.8b00494">emerging viruses</a>. Researchers have used these well-established techniques to test out <a href="https://doi.org/10.1038/s41586-021-03696-9">antibodies after COVID-19 recovery</a>, as well as different vaccines and <a href="https://doi.org/10.1056/NEJMc2113468">different variants</a>. </p>
<p>If antibodies people made against prior variants can’t stop omicron from infecting lung cells in the lab, then those antibodies probably won’t protect people out in the world either.</p>
<p>The very first early results are starting to come back, and it looks like <a href="https://www.ahri.org/wp-content/uploads/2021/12/MEDRXIV-2021-267417v1-Sigal.pdf">antibodies against earlier variants are less successful at blocking omicron</a>. Researchers took antibodies from six people who each had two doses of vaccine and from six other people who each had two doses of vaccine and had also recovered from an earlier COVID-19 infection. Antibodies from both groups of people were about 40 times worse at stopping omicron than original SARS-COV-2 strains, based on how much antibody was needed to prevent infection. But the people whose immune systems had seen the virus three times – that is, were doubly vaccinated and had also recovered from COVID-19 – had antibody levels that were high enough to still stop infection.</p>
<p>I’d expect people who have received booster vaccines will have similar or greater levels of immunity and will be at least moderately protected from omicron. But it will need to be tested. <a href="https://www.pfizer.com/news/press-release/press-release-detail/pfizer-and-biontech-provide-update-omicron-variant">Pfizer has said their early results agree with this prediction</a>, but the data is not yet publicly available. All of this work is not yet peer reviewed and still very preliminary.</p>
<p>Scientists will need to determine how a drop in “neutralization titer,” or how good antibodies are at blocking the virus in the lab, corresponds to a drop in “<a href="https://www.who.int/news-room/feature-stories/detail/vaccine-efficacy-effectiveness-and-protection">vaccine effectiveness</a>” or how likely a vaccinated person is to get COVID-19 compared to an unvaccinated one. Scientists know that <a href="https://doi.org/10.1038/s41591-021-01377-8">better antibodies correspond to more effective vaccines</a>, but the precise numerical relationships need to be determined.</p>
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<h2>How contagious is omicron compared to delta?</h2>
<p>The past pandemic year has shown that contagiousness, or transmissibility, has been the key factor in determining whether a coronavirus variant becomes dominant. Delta’s transmissibility has made it the current dominant variant because it simply outran others. But that situation may change with time.</p>
<p>The basic elements of the viral “life” cycle are getting into cells, making more virus, and getting out. Scientists can measure each of these stages in the lab and <a href="https://www.science.org/doi/10.1126/science.abl6184">report what aspects of a variant</a> make it more or less transmissible. In addition to binding to human cells better, some mutations enhance the packaging of new virus and the delivery of its genes once the virus gets into the cell.</p>
<p>While lab-based science can help people understand the biology behind just why a variant is more or less contagious, right now nature is doing a much bigger real-world experiment. Disease surveillance data from the <a href="https://twitter.com/_nickdavies/status/1466204363110633476?s=20">U.K.</a> and <a href="https://files.ssi.dk/covid19/omikron/statusrapport/rapport-omikronvarianten-07122021-1t6o">other countries</a> where delta has been dominant suggest that omicron is gaining share and may eventually displace delta.</p>
<p>Exactly how this plays out may differ from one country to another, depending on factors like the number of vaccinated people and which variants were previously in circulation, but this news about how good omicron is at spreading is concerning.</p>
<h2>Does omicron make people more or less sick?</h2>
<p>This is again a question that will be answered much more quickly by the thousands of people infected with omicron than by work in the lab. It’s important to remember, though, that nature’s experiments are not as carefully controlled as lab experiments. Precise lab work will help explain why omicron might be different, but the first answers here will come from hospitals.</p>
<p>Lab-based scientists will be working with hospitals to analyze what makes some patients more or less sick once they contract omicron. Some early numbers suggest that the <a href="https://www.samrc.ac.za/news/tshwane-district-omicron-variant-patient-profile-early-features">first omicron cases are mostly mild</a>, but public health officials urge caution: Most cases of all COVID-19 variants are mild, and <a href="https://www.samrc.ac.za/news/tshwane-district-omicron-variant-patient-profile-early-features">many of those infected so far with omicron are younger</a>. Hospitalization counts tend to increase somewhat after the initial increase in cases. So this question will take time to answer.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/436468/original/file-20211208-25-5qjw44.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="nurse attends a COVID-19 patient on a hospital ward" src="https://images.theconversation.com/files/436468/original/file-20211208-25-5qjw44.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/436468/original/file-20211208-25-5qjw44.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/436468/original/file-20211208-25-5qjw44.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/436468/original/file-20211208-25-5qjw44.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/436468/original/file-20211208-25-5qjw44.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/436468/original/file-20211208-25-5qjw44.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/436468/original/file-20211208-25-5qjw44.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">Epidemiological data about how real patients are faring will fill in the picture.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/registered-nurse-attends-a-patient-with-covid-19-at-the-news-photo/1235025034">Apu Gomes/AFP via Getty Images</a></span>
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<h2>How are lab data and public health data complementary?</h2>
<p>Laboratories will provide the first results on immune protection against omicron, although this will be followed up with public health data that will likely confirm the lab results. Public health data will bring the first results on contagiousness and disease severity, which will then be explained by laboratory results.</p>
<p>Once the initial answers from public health data are in, laboratory results are still important to understand why these changes happened and to help predict what future variants will do. How do officials declare a variant of concern in the first place? It’s a combination of public health data and understanding from the lab.</p>
<h2>What do we know already?</h2>
<p>Variants of SARS-CoV-2 don’t change the laws of physics and biology. They cannot leap tall buildings in a single bound. Physical barriers like high-grade masks and good ventilation will still stop the virus. And, very likely, vaccines will continue to provide some amount of protection. The question is how much, and whether the world needs to <a href="https://theconversation.com/how-can-scientists-update-coronavirus-vaccines-for-omicron-a-microbiologist-answers-5-questions-about-how-moderna-and-pfizer-could-rapidly-adjust-mrna-vaccines-172943">change the current vaccines</a> or just provide more of them.</p>
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<p class="fine-print"><em><span>Peter Kasson has received funding from the National Institutes of Health, the National Science Foundation, the Knut and Alice Wallenberg Foundation, the Swedish Research Council, and TG Therapeutics. He is affiliated with the University of Virginia and Uppsala University. </span></em></p>Careful lab work will complement public health data as researchers worldwide focus on omicron, asking questions about contagiousness, severity of disease and whether vaccines hold up against it.Peter Kasson, Associate Professor of Molecular Physiology and Biomedical Engineering, University of VirginiaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1611662021-05-25T12:13:39Z2021-05-25T12:13:39ZCan people vaccinated against COVID-19 still spread the coronavirus?<figure><img src="https://images.theconversation.com/files/402429/original/file-20210524-19-1pkj1h1.jpg?ixlib=rb-1.1.0&rect=0%2C255%2C4788%2C3447&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Vaccinated people are well protected from getting sick, but could they inadvertently transmit the coronavirus?</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/people-walk-in-hudson-river-park-on-may-23-2021-in-new-york-news-photo/1319716519">Noam Galai/Getty Images Entertainment via Getty Images</a></span></figcaption></figure><p><strong>Takeaways:</strong></p>
<ul>
<li>Vaccines can be great at preventing you from getting sick, while at the same time not necessarily stopping you from getting infected or spreading the germ.</li>
<li>Preliminary evidence seems to suggest the COVID-19 vaccines make it less likely someone who’s vaccinated will transmit the coronavirus, but the proof is not yet ironclad.</li>
<li>Unvaccinated people should still be diligent about mask-wearing, physical distancing and other precautions against the coronavirus.</li>
</ul>
<hr>
<p>When the U.S. Centers for Disease Control and Prevention <a href="https://www.whitehouse.gov/briefing-room/press-briefings/2021/05/13/press-briefing-by-white-house-covid-19-response-team-and-public-health-officials-36/">changed its guidelines about mask-wearing</a> on May 13, 2021, plenty of Americans were left a little confused. Now anyone who is fully vaccinated can participate in indoor and outdoor activities, large or small, without wearing a mask or physical distancing.</p>
<p>Anthony Fauci, chief medical adviser to President Biden, said the new guideline is “<a href="https://www.cbsnews.com/news/transcript-dr-anthony-fauci-face-the-nation-05-16-2021/">based on the evolution of the science</a>” and “serves as an incentive” for the <a href="https://covid.cdc.gov/covid-data-tracker/#vaccinations">almost two-thirds of Americans</a> who are not yet fully vaccinated to go ahead and get the shot.</p>
<p>But some people <a href="https://www.cdc.gov/vaccines/covid-19/info-by-product/clinical-considerations.html">cannot be vaccinated</a> because of underlying conditions. Others with weakened immune systems, from cancer or medical treatments, <a href="https://www.medrxiv.org/content/10.1101/2021.03.17.21253131v1">may not be fully protected</a> <a href="https://www.medrxiv.org/content/10.1101/2021.04.06.21254949v1">by their vaccinations</a>. <a href="https://www.fda.gov/news-events/press-announcements/coronavirus-covid-19-update-fda-authorizes-pfizer-biontech-covid-19-vaccine-emergency-use">Children aged 12 to 15 became eligible</a> for the Pfizer-BioNTech vaccine only on May 10, 2021. And <a href="https://www.cdc.gov/vaccines/covid-19/info-by-product/clinical-considerations.html">no COVID-19 vaccines are yet authorized</a> for the nearly <a href="https://www.childstats.gov/americaschildren/tables/pop1.asp">50 million children</a> in the U.S. younger than 12.</p>
<p>As restrictions are lifted and people start to leave their masks at home, some people worry: Can you catch COVID-19 from someone who’s vaccinated?</p>
<h2>Vaccines don’t always prevent infection</h2>
<p>Researchers had hoped to <a href="https://www.fda.gov/regulatory-information/search-fda-guidance-documents/emergency-use-authorization-vaccines-prevent-covid-19">design safe COVID-19 vaccines</a> that would <a href="https://www.fda.gov/media/139638/download">prevent at least half</a> of the people vaccinated from getting COVID-19 symptoms.</p>
<p>Fortunately, the vaccines have <a href="https://doi.org/10.1056/NEJMc2102153">vastly</a> <a href="https://doi.org/10.1016/S0140-6736(21)00947-8">outperformed</a> expectations. For example, <a href="https://doi.org/10.1016/S0140-6736(21)00947-8">in 6.5 million residents of Israel</a>, aged 16 years and older, the Pfizer–BioNTech mRNA COVID-19 vaccine was found to be 95.3% effective after both shots. Within two months, among the 4.7 million fully vaccinated, the detectable infections fell by 30-fold. Similarly in <a href="https://doi.org/10.1056/NEJMc2101927">California</a> and <a href="https://doi.org/10.1056/NEJMc2102153">Texas</a>, only 0.05% of fully vaccinated health care workers tested positive for COVID-19.</p>
<p>Vaccine developers often hope that, in addition to preventing illness, their vaccines will achieve “<a href="https://doi.org/10.1038/srep32973">sterilizing immunity</a>,” where the vaccination blocks the germ from even being able to get into the body at all. This sterilizing immunity means someone who’s vaccinated will neither catch the virus nor transmit it further. For a vaccine to be effective, though, it doesn’t need to prevent the germ from infecting an immunized person. </p>
<p>The <a href="https://www.cdc.gov/vaccines/vpd/polio/index.html">Salk inactivated polio vaccine</a>, for instance, <a href="https://doi.org/10.1016/B978-0-323-04404-2.10092-2">does not completely stop</a> polio virus from growing in the human gut. But it <a href="https://medicine.yale.edu/news/yale-medicine-magazine/breaking-the-back-of-polio/">is extremely effective</a> at preventing the crippling disease because it triggers antibodies that block the virus from infecting the brain and spinal cord. Good <a href="https://doi.org/10.1016/B978-0-323-04404-2.10092-2">vaccines provide effective and durable training</a> for the body’s immune system, so when it actually encounters the disease-causing pathogen, it’s ready to mount an optimum response. </p>
<p>When it comes to COVID-19, immunologists are still figuring out what they call the “<a href="https://doi.org/10.1016/S0140-6736(21)00782-0">correlates of protection</a>,” factors that predict just how protected someone is against the coronavirus. Researchers believe that <a href="https://www.nature.com/articles/s41591-021-01377-8">an optimum amount</a> of “<a href="https://www.sciencedirect.com/topics/neuroscience/neutralizing-antibody">neutralizing antibodies</a>,” the type that not only bind the virus but also prevent it from infecting, are sufficient to fend off <a href="https://doi.org/10.1016/S0140-6736(21)00675-9">repeat infections</a>. Scientists are also still assessing the <a href="https://doi.org/10.1056/NEJMc2032195">durability of immunity</a> that the COVID-19 vaccines are providing and <a href="https://doi.org/10.1101/2021.05.06.21256403">where in the body</a> it’s working. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/402430/original/file-20210524-19-aq22jo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="stickers given out to people who get vaccinated" src="https://images.theconversation.com/files/402430/original/file-20210524-19-aq22jo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/402430/original/file-20210524-19-aq22jo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=384&fit=crop&dpr=1 600w, https://images.theconversation.com/files/402430/original/file-20210524-19-aq22jo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=384&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/402430/original/file-20210524-19-aq22jo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=384&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/402430/original/file-20210524-19-aq22jo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=483&fit=crop&dpr=1 754w, https://images.theconversation.com/files/402430/original/file-20210524-19-aq22jo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=483&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/402430/original/file-20210524-19-aq22jo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=483&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Vaccination can mean far fewer infections, but it’s not clear it will stop transmission by those who are vaccinated.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/stickers-are-stacked-up-for-people-receiving-vaccinations-news-photo/1319347246">Ethan Miller/Getty Images News</a></span>
</figcaption>
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<h2>Can a vaccinated person spread coronavirus?</h2>
<p>Immunologists expect vaccines that protect against viral illnesses to also reduce transmission of the virus after vaccination. But it’s actually tricky to figure out for sure if vaccinated people are not spreading the germ.</p>
<p>COVID-19 poses a particular challenge because people with asymptomatic and pre-symptomatic infections can spread the disease – and insufficient contact tracing and testing mean those without symptoms <a href="https://doi.org/10.1126/science.abf9569">are rarely detected</a>. Some scientists estimate that the number of asymptomatic COVID-19 infections in the overall population <a href="https://doi.org/10.1038/s41467-020-18272-4">could be 3 to 20 times higher</a> than the number of confirmed cases. Research suggests that undocumented cases of COVID-19 in people who either were asymptomatic or experienced very mild disease could be responsible for <a href="https://doi.org/10.1126/science.abb3221">up to 86% of all infections</a>, though other studies <a href="https://doi.org/10.3138/jammi-2020-0030">contradict the high estimates</a>.</p>
<p>In <a href="https://www.cdc.gov/mmwr/volumes/70/wr/mm7013e3.htm?s_cid=mm7013e3_w">one study</a>, the CDC tested volunteer health care personnel and other front-line workers at eight U.S. locations for SARS-CoV-2 infections weekly for three months, regardless of symptoms or vaccination status. The researchers found that fully immunized participants were 25 times less likely to test positive for COVID-19 than were those who were unvaccinated. Findings like this imply that if vaccinated people are so well protected from getting infected at all, they are <a href="https://www.cdc.gov/coronavirus/2019-ncov/science/science-briefs/fully-vaccinated-people.html">also unlikely to spread</a> the virus. But without contact tracing to track transmission in a larger population, it’s impossible to know if the assumption is true.</p>
<p>What we know for sure is that if someone does get sick with COVID-19 after vaccination, in what is called a “breakthrough infection,” <a href="https://doi.org/10.1056/NEJMoa2105000">symptoms will be milder</a>. Studies have found that people who tested positive for COVID-19 after getting <a href="https://www.nature.com/articles/s41591-021-01316-7">just their first vaccine dose</a> had <a href="https://www.medrxiv.org/content/10.1101/2021.02.06.21251283v1">lower levels of virus in their bodies</a> than unvaccinated people who tested positive. The researchers believe the decreased viral load hints that vaccinated people who do contract the virus <a href="https://doi.org/10.1016/S1473-3099(20)30985-3">will be less infectious</a> because they will have much less virus that could be spread to others.</p>
<p>A preprint study which has not yet been peer-reviewed suggests that the Moderna mRNA COVID-19 vaccine can produce coronavirus-fighting <a href="https://doi.org/10.1101/2021.05.06.21256403">antibodies in the oral and nasal fluid</a>. Since <a href="https://doi.org/10.1371/journal.ppat.1009037">that’s where SARS-CoV-2 makes its entry</a>, antibodies in the mouth and nose should block the virus from getting into the body, effectively providing “sterilizing immunity.” This would also mean vaccinated people probably wouldn’t spread the virus through respiratory droplets.</p>
<p>These bits of evidence are promising. But without more studies, scientists <a href="https://doi.org/10.1038/d41586-021-00450-z">cannot yet conclude</a> that COVID-19 vaccines really do protect against all transmission. <a href="https://preventcovidu.org/">Studies attempting</a> to directly answer this question through contact tracing are just beginning: Researchers will track COVID-19 infections among vaccinated and unvaccinated volunteers and their close contacts.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/402431/original/file-20210524-13-5jiayj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="coronavirus precaution signs in multiple languages hang on a fence" src="https://images.theconversation.com/files/402431/original/file-20210524-13-5jiayj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/402431/original/file-20210524-13-5jiayj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/402431/original/file-20210524-13-5jiayj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/402431/original/file-20210524-13-5jiayj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/402431/original/file-20210524-13-5jiayj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/402431/original/file-20210524-13-5jiayj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/402431/original/file-20210524-13-5jiayj.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"></a>
<figcaption>
<span class="caption">CDC guidance still calls for those who are not yet vaccinated to mask up and maintain physical distance.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/wear-a-face-covering-sign-in-three-languages-flushing-news-photo/1310967691">Education Images/Universal Images Group via Getty Images</a></span>
</figcaption>
</figure>
<h2>Protection and prevention go hand in hand</h2>
<p>Vaccines help slow down the spread of an infectious disease by breaking the chain of infection. Those who are infected eventually have fewer and fewer unprotected people to pass the virus on to. This is how a vaccine increases <a href="https://www.who.int/news-room/q-a-detail/herd-immunity-lockdowns-and-covid-19">herd immunity</a> – susceptible and not-yet-immunized people are surrounded by a “herd” of people who have become immune, thanks to vaccination or previous infection. But studies suggest that, for a combination of biological and <a href="https://www.kff.org/coronavirus-covid-19/poll-finding/kff-covid-19-vaccine-monitor-april-2021/">social reasons</a>, <a href="https://doi.org/10.1016/S1473-3099(21)00143-2">vaccination alone is unlikely</a> to achieve herd immunity against COVID-19 and fully contain the coronavirus.</p>
<p>In fact, vaccination <a href="https://doi.org/10.1146/annurev.publhealth.20.1.211">alone can take a long time</a> to eradicate any disease. Even diseases that are nearly “eliminated” – such as chickenpox, measles and pertussis – <a href="https://doi.org/10.1001/jama.2016.1353">can resurface</a> with waning immunity and declining vaccine rates. </p>
<p>The recent outbreak of infections among the <a href="https://www.npr.org/2021/05/14/996873507/what-to-make-of-the-yankees-outbreak-scientists-say-dont-panic-we-expected-this">vaccinated New York Yankees</a> shows that vaccinated people not only can still get infected, they might also transmit the coronavirus to close contacts. Highly tested groups, such as professional sports teams, spotlight the fact that mild, asymptomatic infections among the vaccinated in the general population might actually be more frequent than reported. A similar <a href="https://www.straitstimes.com/singapore/speed-at-how-changi-airport-covid-19-cluster-grew-is-worrying-says-expert">outbreak in airport workers in Singapore</a> shows that, even among the fully vaccinated, new and more infectious variants can spread fast. </p>
<p>The CDC’s relaxed guidelines on masking are meant to reassure vaccinated people that they are safe from serious illness. And they are. But the picture is less clear-cut for the unvaccinated who interact with them. Until near herd immunity against COVID-19 is achieved, and clear evidence accumulates that vaccinated people do not spread the virus, I and <a href="https://www.nytimes.com/2021/05/13/upshot/epidemiologists-coronavirus-masks.html">many epidemiologists</a> believe it is better to avoid situations where there are chances to get infected. Vaccination coupled with <a href="https://www.pnas.org/content/118/4/e2014564118">continued masking</a> and social distancing is still an effective way to stay safer.</p>
<p>[<em><a href="https://theconversation.com/us/newsletters/science-editors-picks-71/?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=science-corona-important">The Conversation’s most important coronavirus headlines, weekly in a science newsletter</a></em>]</p><img src="https://counter.theconversation.com/content/161166/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sanjay Mishra receives funding from the National Cancer Institute through his institution. </span></em></p>The COVID-19 vaccines are a smash success. But that doesn’t mean they keep every vaccinated person completely free of the coronavirus.Sanjay Mishra, Project Coordinator & Staff Scientist, Vanderbilt University Medical Center, Vanderbilt UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1557122021-03-25T12:26:42Z2021-03-25T12:26:42ZWhy you should get a COVID-19 vaccine – even if you’ve already had the coronavirus<figure><img src="https://images.theconversation.com/files/391257/original/file-20210323-2308-kn86fb.jpg?ixlib=rb-1.1.0&rect=314%2C233%2C4778%2C3862&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Vaccination produces a much stronger and more consistent immune response than infection.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/covid-19-vaccine-circular-pattern-royalty-free-image/1287876073?adppopup=true"> Andriy Onufriyenko/Moment via Getty Images</a></span></figcaption></figure><p>A few weeks ago, a message popped up in the corner of my screen. “What do you think about people who have recently had COVID–19 getting the vaccine?” A friend of mine was eligible for a COVID–19 vaccine, but she had recently gotten over an infection with SARS–CoV–2. More people are becoming eligible for vaccines each week – including millions of people who have already <a href="https://www.cdc.gov/coronavirus/2019-ncov/covid-data/covidview/index.html">recovered from a coronavirus infection</a>. Many are wondering whether they need the vaccine, especially people who have already been infected.</p>
<p><a href="https://scholar.google.com/citations?user=MEMHuGoAAAAJ&hl=en&oi=ao">I study immune responses to respiratory infections</a>, so I get a lot of these types of questions. A person can develop immunity – the ability to resist infection – from being infected with a virus or from getting a vaccine. However, immune protection isn’t always equal. The strength of the immune response, the length of time that the protection lasts and the variation of the immune response across people is very different between vaccine immunity and natural immunity for SARS–CoV–2. COVID–19 vaccines offer safer and more reliable immunity than natural infection. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/391258/original/file-20210323-13-vbg1w4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Electron microscope image of four SARS–CoV–2 particles" src="https://images.theconversation.com/files/391258/original/file-20210323-13-vbg1w4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/391258/original/file-20210323-13-vbg1w4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=469&fit=crop&dpr=1 600w, https://images.theconversation.com/files/391258/original/file-20210323-13-vbg1w4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=469&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/391258/original/file-20210323-13-vbg1w4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=469&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/391258/original/file-20210323-13-vbg1w4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=589&fit=crop&dpr=1 754w, https://images.theconversation.com/files/391258/original/file-20210323-13-vbg1w4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=589&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/391258/original/file-20210323-13-vbg1w4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=589&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The immune system will usually generate an immune response to a SARS-CoV-2 infection, but not always.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Novel_Coronavirus_SARS-CoV-2.jpg#/media/File:Novel_Coronavirus_SARS-CoV-2.jpg">National Institutes of Allergy and Infectious Diseases</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Immunity after infection is unpredictable</h2>
<p>Immunity comes from the immune system’s ability to remember an infection. Using this immune memory, the body will know to fight if it encounters the disease again. Antibodies are proteins that can bind to a virus and prevent infection. T cells are cells that direct the removal of infected cells and viruses already bound by antibodies. These two are some of the main players that contribute to immunity.</p>
<p>After a SARS-CoV-2 infection, a person’s antibody and T cell responses may be strong enough to provide <a href="https://doi.org/10.1126/science.abf4063">protection against reinfection</a>. Research shows that 91% of people who develop antibodies against the coronavirus are unlikely to be infected again <a href="https://doi.org/10.1056/NEJMoa2034545">for six months</a>, even after <a href="https://doi.org/10.1016/j.cell.2020.11.029">a mild infection</a>. People who had no symptoms during the infection are also likely to develop immunity, though they tend to make <a href="https://doi.org/10.1038/s41564-020-00813-8">fewer antibodies</a> than those who felt ill. So for some people, natural immunity may be strong and long-lasting. </p>
<p>The problem is that not everyone will develop immunity after a SARS-CoV-2 infection. As many as 9% of infected people do not have <a href="https://doi.org/10.1056/NEJMoa2026116">detectable antibodies</a>, and up to 7% of people <a href="https://doi.org/10.1126/science.abf4063">don’t have T cells that recognize the virus</a> 30 days after infection. </p>
<p>For people who do develop immunity, the <a href="https://doi.org/10.1038/s41586-020-2456-9">strength and duration</a> of the protection can vary a lot. Up to 5% of people may <a href="https://doi.org/10.1126/science.abf4063">lose their immune protection</a> within a few months. Without a strong immune defense, these people are susceptible to reinfection by the coronavirus. Some have had second bouts of COVID–19 as soon as <a href="https://doi.org/10.1002/jmv.26637">one month after their first infection</a>; and, though rare, some people have been <a href="https://doi.org/10.1016/j.jinf.2021.01.020">hospitalized or even died</a>. </p>
<p>A person who is reinfected may also be able to transmit the coronavirus even <a href="https://doi.org/10.1001/jamanetworkopen.2020.35057">without feeling sick</a>. This could put the person’s loved ones at risk. </p>
<p>And what about the variants? So far, there isn’t any hard data about the new coronavirus variants and natural immunity or reinfection, but it is certainly possible that immunity from one infection won’t be as strong against infection with a different variant.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/391251/original/file-20210323-21-w4qpa2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A healthy human T cell, a large blue rumpled sphere" src="https://images.theconversation.com/files/391251/original/file-20210323-21-w4qpa2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/391251/original/file-20210323-21-w4qpa2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/391251/original/file-20210323-21-w4qpa2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/391251/original/file-20210323-21-w4qpa2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/391251/original/file-20210323-21-w4qpa2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/391251/original/file-20210323-21-w4qpa2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/391251/original/file-20210323-21-w4qpa2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">COVID–19 vaccines produce a strong immune response in terms of both antibodies and T cells, like the T cell in this photo.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Healthy_Human_T_Cell.jpg#/media/File:Healthy_Human_T_Cell.jpg">National Institutes of Allergy and Infectious Diseases/National Institutes of Health</a></span>
</figcaption>
</figure>
<h2>Vaccination leads to reliable protection</h2>
<p>COVID–19 vaccines generate both <a href="https://doi.org/10.1056/NEJMoa2022483">antibody and T cell responses</a> – but this is much stronger and more consistent than immunity from natural infection. One study found that four months after receiving their first dose of the Moderna vaccine, <a href="https://doi.org/10.1056/NEJMc2032195">100% of people tested had antibodies against SARS-CoV-2</a>. This is the longest period that has been studied so far. In a study looking at the Pfizer and Moderna vaccines, antibody levels were also much higher in vaccinated people than in those who had <a href="https://doi.org/10.1056/NEJMoa2028436">recovered from infection</a>.</p>
<p>Even better, a <a href="https://doi.org/10.1056/NEJMoa2101765">study in Israel</a> showed that the Pfizer vaccine blocked 90% of infections after both doses – even with a variant present in the population. And a <a href="https://doi.org/10.1093/cid/ciab229">decrease in infections</a> means people are less likely to transmit the virus to the people around them.</p>
<p>The COVID–19 vaccines aren’t perfect, but they produce strong antibody and T cell responses that offer a safer and more reliable means of protection than natural immunity.</p>
<h2>Infection and vaccination together</h2>
<p>To my friend’s message, I instantly replied that she should absolutely get the vaccine. After getting vaccinated, my friend could be comfortable knowing that she has long-lasting, effective immunity and less of a chance of spreading the coronavirus to her friends and family. </p>
<p>But more good news has emerged since I sent that message. A new study showed that vaccination after infection produces <a href="https://doi.org/10.1056/NEJMc2101667">six times more antibodies</a> than a vaccine by itself. This isn’t to say that anyone should try to get infected before they get vaccinated – vaccine immunity alone is more than strong enough to provide protection and the dangers of a fight with COVID-19 far outweigh the benefits. But when my friend and the many others who were already infected get their vaccines, they’ll be well protected.</p>
<p>Natural immunity from infection is simply far too unreliable in the face of such a devastating virus. Current COVID-19 vaccines offer incredibly strong, consistent protection to the great majority of people. So, for anyone eligible, even those who have already had a SARS-CoV-2 infection, COVID-19 vaccines offer immense benefits.</p>
<p>[<em>Get facts about coronavirus and the latest research.</em> <a href="https://theconversation.com/us/newsletters/the-daily-3?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=coronavirus-facts">Sign up for The Conversation’s newsletter.</a>]</p><img src="https://counter.theconversation.com/content/155712/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jennifer T. Grier does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>If you’ve already had the coronavirus and recovered, you might be tempted to give the vaccine a pass. A scientist explains why the shot offers the best protection against future infection.Jennifer T. Grier, Clinical Assistant Professor of Immunology, University of South CarolinaLicensed as Creative Commons – attribution, no derivatives.