On May 20, disease modelers at Columbia University posted a preprint that concluded the US could have prevented 36,000 of the 65,300 deaths that the country had suffered as a result of COVID-19 by May 3 if states had instituted social distancing measures a week earlier. In early June, Imperial College London epidemiologist Neil Ferguson, one of the UK government’s key advisers in the early stages of the pandemic, came to a similar conclusion about the UK. In evidence he presented to a parliamentary committee inquiry, Ferguson said that if the country had introduced restrictions on movement and socializing a week sooner than it did, Britain’s official death toll of 40,000 could have been halved.
On a more positive note, Ferguson and other researchers at Imperial College London published a model in Nature around the same time estimating that more than 3 million deaths...
These and other studies from recent months aim to understand how well various social-distancing measures have curbed infections, and by extension saved lives. It’s a big challenge to unravel and reliably understand all the factors at play, but experts say the research could help inform future policies.
The most effective measure, one study found, was getting people not to travel to work, while school closures had relatively little effect.
“It’s not just about looking retrospectively,” Jeffrey Shaman, a data scientist at Columbia University and coauthor of the preprint on US deaths, tells The Scientist. “All the places that have managed to get it under control to a certain extent are still at risk of having a rebound and a flare up. And if they don’t respond to it because they can’t motivate the political and public will to actually reinstitute control measures, then we’re going to repeat the same mistakes.”
Diving into the data
Shaman and his team used a computer model and data on how people moved around to work out how reduced contact between people could explain disease trends after the US introduced social distancing measures in mid-March. Then, the researchers looked at what would have happened if the same measures had been introduced a week earlier, and found that more than half of total infections and deaths up to May 3 would have been prevented. Starting the measures on March 1 would have prevented 83 percent of the nation’s deaths during that period, according to the model. Shaman says he is waiting to submit for publication in a peer-reviewed journal until he and his colleagues update the study with more-recent data.
“I thought they had reasonably credible data in terms of trying to argue that the lockdowns had prevented infections,” says Daniel Sutter, an economist at Troy University. “They were training or calibrating that model using some cell phone data and foot traffic data and correlating that with lockdowns.”
Sébastien Annan-Phan, an economist at the University of California, Berkeley, undertook a similar analysis, looking at the growth rate of case numbers before and after various lockdown measures were introduced in China, South Korea, Italy, Iran, France, and the US. Because these countries instituted different combinations of social distancing measures, the team was able to estimate how well each action slowed disease spread. The most effective measure, they found, was getting people not to travel to work, while school closures had relatively little effect. “Every country is different and they implement different policies, but we can still tease out a couple of things,” says Annan-Phan.
In total, his group estimated that combined interventions prevented or delayed about 62 million confirmed cases in the six countries studied, or about 530 million total infections. The results were published in Nature in June alongside a study from a group at Imperial College London, which had compared COVID-19 cases reported in several European countries under lockdown with the worst-case scenario predicted for each of those countries by a computer model in which no such measures were taken. According to that analysis, which assumed that the effects of social distancing measures were the same from country to country, some 3.1 million deaths had been avoided.
It’s hard to argue against the broad conclusion that changing people’s behavior was beneficial, says Andrew Gelman, a statistician at Columbia University. “If people hadn’t changed their behavior, then it would have been disastrous.”
Lockdown policies versus personal decisions to isolate
Like all hypothetical scenarios, it’s impossible to know how events would have played out if different decisions were made. And attributing changes in people’s behavior to official lockdown policies during the pandemic is especially difficult, says Gelman. “Ultimately, we can’t say what would have happened without it, because the timing of lockdown measures correlates with when people would have gone into self-isolation anyway.” Indeed, according to a recent study of mobile phone data in the US, many people started to venture out less a good one to four weeks before they were officially asked to.
A report on data from Sweden, a country that did not introduce the same strict restrictions as others in Europe, seems to support that idea. It found that, compared with data from other countries, Sweden’s outcomes were no worse. “A lockdown would not have helped in terms of limiting COVID-19 infections or deaths in Sweden,” the study originally concluded. But Gernot Müller, an economist at the University of Tubingen who worked on that report, now says updated data show that original conclusion was flawed. Many Swedes took voluntary actions in the first few weeks, he says, and this masked the benefits that a lockdown would have had. But after the first month, the death rate started to rise. “It turns out that we do now see a lockdown effect,” Müller says of his group’s new, still unpublished analyses. “So lockdowns do work and we can attach a number to that: some 40 percent or 50 percent fewer deaths.”
Some critics question the assumption that such deaths have been prevented, rather than simply delayed. While it can appear to be a semantic point, the distinction between preventing and delaying infection is an important one when policymakers assess the costs and benefits of lockdown measures, Sutter says. “I think it’s a little misleading to keep saying these lockdowns have prevented death. They’ve just prevented cases from occurring so far,” he says. “There’s still the underlying vulnerability out there. People are still susceptible to get the virus and get sick at a later date.”
Shaman notes, however, that it’s really a race against the clock. It’s about “buying yourself and your population critical time to not be infected while we try to get our act together to produce an effective vaccine or therapeutic.”