UCL News


Opinion: When should we lift the coronavirus lockdown?

22 April 2020

Dr Jasmina Panovska-Griffiths (UCL Epidemiology & Health) comments on UK lockdown procedures, the possibility of a second wave and when the lockdown might ease.

Dr Jasmina Panovska-Griffiths

The world is watching closely following the lifting of the public lockdown in the city of Wuhan, where the coronavirus pandemic started. The metropolitan-wide quarantine was in place for 76 days since January 23, and restrictions were seemingly effective, with the daily reported confirmed cases of COVID-19 significantly reduced from 1,500-2,000 at the peak to 10 cases or fewer a day now.

Meanwhile, those of us in or heading towards our second month of lockdown are starting to wonder when it will be our turn to lift or relax restrictions. This is especially true for countries where the spread of the virus, related hospitalisations and deaths are showing signs of slowing down.

The lifting of the lockdown in Wuhan followed a gradual easing of the restrictions by allowing residents to leave their residences on a limited basis. But importantly, this was combined with a massive screening programme to test people at high risk from the disease or anyone who had been in close contact with infected patients. This enabled authorities to contain the infection and reduce the number of cases by 90%.

Similarly, lifting the lockdown in other countries will depend on their ability to contain the virus and protect the public once restrictions have gone. To asses this and decide when to end the lockdown, we need to answer three questions.

First, have we suppressed the spread of the virus enough so that it won’t produce a second surging wave of infections and deaths in the future? Answering yes to this is the most pressing item. It requires us to be sure that we have passed the peak of the disease, that infections are declining and that we haven’t just temporarily suppressed the spread.

In mathematical modelling terms, this requires the average number of people to which every infected person spreads the virus (known as the basic reproduction number or R0) to fall to and remain less than 1. The estimated value of R0 for COVID-19 spreading through the population without restrictions is between 2 and 3. Bringing this number below 1 will lead to fewer people catching the disease than recovering from it, so the number of new infections will decline and the epidemic will die out.

Lockdown effects

This is where the lockdown and social distancing come in. Modelling studies suggest that travel restrictions in Wuhan brought R0 down from 2.35 to 1.05 in two weeks. For the UK, an initial analysis suggests that R0 has dropped by 73% since the lockdown began.

But another recent paper modelled the spread of the virus in China outside of Hubei province where Wuhan is located. It showed that relaxing the lockdown too early would mean R0 would exceed 1 after restrictions are lifted and lead to a second wave of infections.

There are indications that some countries may be reaching the peak of the virus, but realistically it will be a while before we can be certain this is not just a temporary suppression. This is because there may be possible delays in the reported number of infections and deaths.

Importantly, by stopping the spread of the virus with current social distancing measures, we aren’t just preventing people from dying. We are also buying time for scientists to learn more about the disease and its pattern of spread, and to work on producing an effective vaccine.

This brings us to the second question. Can we identify all infections and prevent new infections emerging? To do this, we need to make sure everyone who has the disease is in isolation. Then we need a way to trace everyone they have recently come into contact with to see if they too need to be isolated.

But we also need to know whether people can carry the virus without showing any symptoms of the disease. Recent studies have suggested that this may be the case. But to be sure we need to urgently undertake large-scale antibody testing of the population.

Looking for antibodies in the blood that the body has produced in response to the virus will tell us who has had it and give us a more realistic picture of its spread. There are already antibody tests available and more in development, but it’s not yet clear that they are accurate enough for a reliable mass-screening programme. Only when this is possible can we make sure that no new infections can emerge from undiagnosed cases.

Second wave

Finally, there’s the question of what would happen if a second wave occurred once restrictions were lifted. The only way to be sure the public would be fully protected is with effective antiviral drugs or a vaccine against the virus. Although progress has been made in this direction, an effective vaccine appears many months away.

If we want to lift the lockdown before then, we must make sure we have a strategy that will minimise the risk of a secondary pandemic wave that could cause more deaths. Second waves occurred in all four respiratory pandemics of the past century, in some cases killing more than the initial waves.

One way to do this would be to follow Wuhan’s example of continuing some social distancing measures and protecting the most vulnerable after the strictest elements of the lockdown have been lifted. At the same time, we need to continue monitoring and modelling the disease to ensure we catch any second wave at its onset and act quickly to prevent its spread.

But before we get to this point, we still need to be sure we have passed the peak of the disease’s spread and introduce a mass testing and contact-tracing programme to identify and contain any remaining infections. And for many countries, that could still be weeks – if not months – away.

This article was originally published in The Conversation on 17 April.