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People celebrating Christmas over video conferencing, as shown on the screen of a laptop.

Why the government was right to introduce Tier 4 restrictions

A new, potentially more infectious variant of the coronavirus is thought to be behind rising COVID-19 case numbers in southern parts of the UK. Fearing this version of the virus could spread out of control, the government has introduced a stricter level of restrictions across much of England: Tier 4.

In Tier 4 areas – which include London and much of the south-east – people must stay at home unless they have a permitted reason not to, such as going to work or exercising. Travel, when permitted, should be kept to a minimum. And indoor mixing has been banned, with the mixing of households at Christmas no longer allowed.

With millions of people’s Christmases disrupted, many will be asking why the rules needed to change so quickly. Here’s what the evidence tells us about why the decision to introduce Tier 4 was made, as well as what the effects of these restrictions might be and how long living under them may last.

Increased infectiousness looks likely

The new strain of the coronavirus contains a suite of mutations, and has been spreading rapidly in London and the south-east of England. It’s also been found in all other parts of the UK as well as in a small number of cases in Denmark, the Netherlands and Australia.

Whenever a virus mutates, there are three key questions: does it cause more severe disease? Is it different enough to evade existing immunity or vaccines? And is it more infectious?

We don’t yet have definitive answers to any of these questions, but there’s evidence that concludes with some confidence that this variant is more transmissible. Some of its mutations involve the spike protein and receptor binding areas – key parts of the virus that help it get inside cells – and accordingly there are indications that the virus’s ability to infect human cells has increased.

SARS-CoV-2 binding to an ACE2 receptor
The spike proteins (orange) on the surface of SARS-CoV-2 bind to ACE2 (green) to allow the virus entry into the cell. Kateryna Kon/Shutterstock

This then seems to lead both to people having more of the virus in their system (known as viral load) and an increase in R (the reproduction number, or number of people an infected person goes on to infect) of between 0.4 and 0.9, which is then suspected of driving up case numbers.

Case numbers needed to be slowed

This is what we know so far, but it will take weeks to confirm all the characteristics of this variant – including the precise mechanisms behind the suspected increase in transmission, as well as the age distribution and severity of cases it causes.

Quite rightly, the UK government has moved swiftly to increase restrictions on social mixing and movement in areas where the strain is prevalent. Other countries in Europe and further afield, also out of caution, have temporarily limited international travel from the UK.

The measures available to control spread of this variant are the same as for COVID-19 more generally – reduce social contact, wear face masks and regularly wash hands. But the fact that this variant has spread during a period of existing social restrictions in the UK is worrying, and underscores why there was a need to strengthen control measures and encourage greater compliance.

It was already clear, before the announcement of this strain, that only the highest tier of restrictions in England was controlling transmission. Scientists had already been advising the government to abandon its plan to allow greater social freedoms over Christmas, as had been done in other European countries. Indeed, even if this variant turns out not to be more transmissible, the fast-increasing number of COVID-19 cases that we’ve seen recently, with a doubling time of six to seven days, means that tighter restrictions were needed urgently anyway.

It’s not known yet whether the Tier 4 measures will be effective in bringing the virus’s reproduction number below 1 and so stop case numbers from rising or whether even stricter measures, such as a full lockdown as happened in March, will be needed. The restrictions may need to extended to more parts of the country, given that we know the variant is already seeded throughout the UK.

A sign displaying Tier 4 rules at King's Cross station in London
Tier 4 rules will be reviewed on December 30 2020, but may last much longer. EPA-EFE

Wide compliance and support from the general public will be of key importance in ensuring the maximum effectiveness of these measures. Commentators have stressed the need for every individual to assume that they are infectious and to modify their behaviour accordingly.

It’s likely that these measures will need to be in place in the UK for several weeks to bring down the absolute numbers of new cases and reduce pressure on the NHS. This will also give the case detection and contract tracing system a chance to be effective, and will buy time for the COVID-19 vaccination programme to reach a substantial proportion of the at-risk population.

During the first wave of the pandemic, and more recently in places such as Melbourne, Australia, lockdowns of around three months were needed to really gain control of the epidemic. Other countries will be watching the situation in the UK very closely, to see if the same applies in this situation.

Overall, it looks like it is going to be an even harder winter in the UK than anticipated, but with the expansion of vaccination, by the time the weather starts to warm, we may be over the worst. It is up to everybody in all walks of life to take individual responsibility for controlling this epidemic, which affects us all.

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