Researchers predict best strategy for lifting COVID-19 lockdowns

As the first wave of the COVID-19 pandemic wanes in many parts of the world, some countries are relaxing lockdown rules, but several are encouraging non-essential workers to continue to work from home. A new study published in the journal Frontiers in Public Health explores how and when lockdowns should be lifted for non-essential workers.

For the study, the researchers showed that a gradual strategy with two discrete releases of subgroups of the quarantined population would be optimal for society as a whole to minimize deaths while protecting the economy.

The researchers modeled the numbers of susceptible, exposed, infectious, and recovered or deceased persons in the United Kingdom, separately for those under lockdown and those working as normal. They derived a strategy for releasing people from lockdown, requiring that the greatest number should be allowed to work as soon as possible, while maintaining social distancing, but without overwhelming the health services, estimated to happen when there are approximately 4 million infected people in the United Kingdom. The model was kept as simple as feasible, not only to make results easier to interpret, but also to allow it to be easily applied to other countries.

The researchers concluded that the optimal strategy would be to release approximately half the population two to four weeks from the end of an initial infection peak, and then wait another three to four months to allow for a potential second peak to pass before releasing everyone else. The optimal solution depends partly on the poorly known rate at which people sick with COVID-19 recover and the rate of viral transmission, but hardly on the death rate, the incubation period, or the effectiveness of lockdown measures.

While the model itself does not prescribe which people should be released from lockdown first, the authors suggest that this should be the younger part of the population, known to be less susceptible to COVID-19, provided that they are closely monitored with molecular tests, as they would be at increased risk.

"The take-home message for decision-makers is to act very cautiously, and to monitor any lockdown release very closely,” said Thomas Rawson, PhD, first author of the study from the University of Oxford, in a statement. “Our model shows that second waves can occur very quickly if transmission rates end up higher than expected, or if more people relax their lockdown measures than expected. The delayed incubation period between infection and presenting symptoms means that we are constantly seeing the effect of the disease a few days late. Only by ramping up testing measures can we accurately get a sense of how the spread and control of disease is happening. This will allow us to respond quickly if an unmanageable second wave begins to appear.”

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