New Mathematical Model Could Improve Worldwide Pandemic Responses

People line up last month in front of medical workers to take swabs as part of coronavirus testing in Wuhan, in central China’s Hubei province. (Chinatopix Via AP)

(CN) — British researchers on Wednesday published a mathematical model that can help policymakers determine the optimal path to lifting lockdown measures in a way that balances economic recovery and public health during the Covid-19 crisis.

Scholars at Oxford University and the U.K. Centre for Ecology and Hydrology used data from the United Kingdom to find that ending quarantine in two stages — permitting certain nonessential workers to go back to work while having others hold out for months before doing the same — would improve economic output without overburdening Britain’s healthcare system, while an all-at-once lockdown lift risks catastrophe.

“We find that ending quarantine for the entire population simultaneously is a high-risk strategy, and that a gradual re-integration approach would be more reliable,” write the authors, whose research is published today in Frontiers in Public Health.

The group, led by Oxford population biologist Michael Bonsall, examined data on Britons who are susceptible to infection, who have already been infected and how many either recovered or died. Then they tested two approaches the U.K. could take to end the nation’s lockdown without pushing its health services past the breaking point.

The first strategy, “gradual release,” would permanently take waves of the nonessential working population out of quarantine.The second option, “on-off release,” mirrors many nations’ present strategy: lockdown regulations are lifted for everyone at the same time, but reinstated if infections spike again.

According to their models, an optimal outcome is possible if about half of nonessential British workers are released between two and four weeks after the end of an initial infection peak, and everyone else is released between three and four months later — time enough for a second peak to pass, if it comes.

The researchers say the alternative — an “on-off” strategy that releases everyone from lockdown at once but reintroduces restrictions if infections go out of control — risks an unmanageable worst-case scenario that would surpass the U.K.’s capacity to handle roughly four million patients.

“A population-wide instantaneous release would cause the number of infected individuals to rise dramatically, in a short period of time,” the authors write in their paper.

But this conclusion is somewhat conditioned: the authors acknowledge that the Covid-19 recovery rate is uncertain, and the rate of transmission could rise and undercut the effectiveness of a two-tiered approach.

The authors also note that the jury is still out as to whether people who have recovered from Covid-19 are immune from future infections, or if they remain susceptible to suffering a second coronavirus infection. Their model assumes the infected acquire immunity, but this is not yet known.

Though the research took up British data to evaluate two strategies for reopening Britain, researchers across the world can plug local information into the model to find the best approach for other regions.

“The very cool thing about this model is that it’s completely applicable to anywhere. So you can do it in Texas, you can do it across the U.S., you can do it as we did across the U.K.,” said Bonsall, the lead author. “It will give you an opportunity to figure out what the local release-from-lockdown strategy should be. That’s the real value of this sort of modeling, it’s very generic.”

Bonsall was adamant that policymakers should take heed to not only his group’s research, but the research of others as well.

“It’s only one piece of work, it’s only one piece of evidence in the big jigsaw of solving this problem,” Bonsall said. “To hang all of your hopes on one piece of work, and for decision-makers to make advances based on one piece of work is just tantamount to failure. It’s just a very dangerous thing to do.”

Thomas Rawson, an Oxford researcher and one of the study’s five co-authors, shared a similar sentiment.

“The take-home message for decision-makers is to act very cautiously, and to monitor any lockdown release very closely,” said Rawson. “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.”

While the model does not itself suggest which part of the population should be released first, the authors opine that younger people, who are less likely to suffer the deadliest complications of a Covid-19 infection, should be the first out of lockdown — if public health officials can closely monitor them, that is.

“Only by ramping up testing measures can we accurately get a sense of how the spread and control of disease is happening,” Rawson said. “This will allow us to respond quickly if an unmanageable second wave begins to appear.”

Bonsall, the lead author, said he hopes the group’s models can help direct other nations’ pandemic strategies.

“Exactly what happens as lockdown eases can be hard to predict, as different people will respond in different ways. However, when a large enough group of people is considered, mathematical models like ours are able to represent the expected average behaviors across a large population,” Bonsall said. “Ongoing testing is then important to check that any disease increase does not surpass the predicted bounds.”

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