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It isn’t safe to lift lockdowns until new case numbers are low

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By April this year, around half of the world’s population was under some kind of lockdown. Such restrictions helped slow the spread of the coronavirus. As new cases decline in many places, countries are beginning to ease restrictions. How can we know it is safe to do so?

The World Health Organization’s principal recommendation is that, in order to move to a sustainable level of virus transmission, countries should have the spread of the virus under control. In practice, this means seeing a robust decline in the number of cases.

The WHO also advises that countries use testing and contact tracing to identify and isolate new cases of covid-19. Without screening and isolation, easing restrictions will inevitably lead to the number of new infections rising again. The UK government appears to be on course to restart contact tracing imminently, after controversially abandoning it in March, although details are scarce.

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Yet to ease restrictions, a country’s number of cases also needs to be at a manageable level, says Christina Pagel at University College London. A lot of attention has been paid to the R, or reproduction number: the number of people each person with the virus is likely to infect. If this is above one, cases will continue to rise exponentially, so the aim is to keep it below this. But that alone isn’t enough, says Pagel.

“Say you have an R of just less than one. That will give you a stable level of infection,” says Pagel. “But if that stable level of infection is thousands a day, that’s not really going to help you – you’re going to end up with a really burdened health system.”

The UK government reported 2684 positive test results on 18 May, and 2412 on 19 May.

Even when new case numbers are low, lifting restrictions will always carry a risk of a second wave of infections. South Korea brought its outbreak under control with a stringent policy of testing, isolation and contact tracing. In recent weeks, the country was reporting only around 10 new cases per day. However, following eased restrictions from 6 May, the Korea Centers for Disease Control and Prevention last week confirmed 102 new cases linked to nightclubs in Seoul. As a result, some clubs and bars have been ordered to close again.

There are concerns that similar outbreaks might occur in Germany, thanks to the gradual lifting of restrictions since the end of April. Germany’s early response to the virus and mass testing strategy brought the country’s R down from more than three to just below one during March. But last week, between 407 and 927 new cases were reported every day, and estimates from the Robert Koch Institute in Berlin suggest that the R may have risen above one since 6 May.

In Wuhan, China, five new cases of the virus were reported on 10 May, after the city where the global outbreak started eased some restrictions in early April. However, other than a handful of cases, there doesn’t appear to have been a second wave of infections.

It is unlikely that any country exiting lockdown will return to how things were before the outbreak. Social distancing, regular handwashing and, in some places, face masks may become a new normal. “There’s an assumption that we can get to a point and then relax,” says Paul Hunter at the University of East Anglia, UK. “That’s a false assumption.”

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