coronavirus covid-19 shelter in place stay at home social distancing physical isolation modeling
coronavirus covid-19 shelter in place stay at home social distancing physical isolation modeling

The Effects of Physical Isolation on the Pandemic Quantified

Social distancing measures are based on limited data. As much of the world remains stuck in lockdown, researchers are trying to measure the benefits.

David Adam
David Adam

David Adam is a freelance science journalist and a bestselling author based in the UK.

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Apr 10, 2020

ABOVE: A playground in Maumee, Ohio, where the governor’s stay-at-home order went into effect March 23

In July 2008, some 400 young people from the Solomon Islands visited Sydney, Australia, for a Catholic youth festival. Short on accommodations—the week-long event drew 223,000 pilgrims from across the world—the Solomon Islanders bedded down in the cavernous gym of a local school. Within days, a spate of fever, headaches, and coughing fits signaled to organizers that they had a serious problem. An influenza outbreak had ripped through the closely quartered group, eventually making more than one-fourth of them unwell.

A large group of Australians were also staying at the school and passing around the virus. But far fewer of them became ill—just 27 of the 255. What protected them?

In turned out the Australians had slept in groups of eight, each isolated in their own classroom.

Health officials treated everyone and mopped up the Sydney outbreak within a week or so. But that limited incident had a lasting impact on the infectious disease community. Written up as a study three years later in an obscure Australian government journal called Communicable Disease Intelligence, it’s one of the few proven examples of the benefits that social and physical distancing measures can have against a contagious virus. As such, it’s a key part of what researchers at the Centre for Evidence-Based Medicine at the University of Oxford admit is “limited” evidence available to support social-distancing measures as a response to the ongoing pandemic. Alongside studies of how different cities dealt with the 1918 flu pandemic that killed millions of people around the world, all those sick worshippers camped out in a school are part of the reason you are in lockdown.

Google data from smart phone users show that visits to shops, museums, and cafes in the UK have fallen by 85 percent.

Social distancing worked then. So how is it working now to contain the ongoing COVID-19 pandemic? The answer comes down to two questions: Are people behaving as they are expected to? And do those behavioral changes subsequently reduce transmission of the disease as predicted?

On the first, Mirco Tonin, an economist at the Free University of Bozen-Bolzano in Italy, has asked nearly 900 people in the country about their lockdown behavior in recent weeks. His results indicate most people are complying with requests to stay at home. Or at least about half the people who responded to the survey say that’s what they are doing. Although Tonin is usually suspicious of data from self-reported surveys on wrong-doing, in this case, he tends to believe the respondents.

“If you ask people about tax evasion you get zero and that’s clearly not true. If you ask if they cheat on their husbands or wives, then they don’t like to admit it,” he tells The Scientist. “But here we were asking, are you meeting your friends, are you meeting your relatives, and those are behaviors that are socially acceptable. So people were probably more likely to admit they were doing it.”

Stefan Pfattheicher, a psychologist at Aarhus University in Denmark, surveyed more than 2,000 people across the UK, US, and Germany in mid-March and got similar results. “More than 50 percent of all participants say they do the maximum asked of them,” he says. And questionnaires in China show that citizens of Wuhan and Shanghai reported between seven and nine times fewer daily contacts with other people than was typical.

Other data support the conclusion that people are staying at home. Earlier this month, Google released location data harvested (and anonymized) from smart phone users across the world. They show, for example, that visits to shops, museums, and cafes in the UK have fallen by 85 percent. In the US, such activity has dropped by 47 percent.

The second question—how much does all this social distancing reduce transmission—is harder to answer with real data. That’s because there’s typically a three-week lag between infection and people dying, which, without comprehensive testing, remains the most reliable indicator of disease spread.

Researchers in Hong Kong have tried to address this dearth of data using a statistical trick called “nowcasting” to estimate a real-time measure of how the virus is spreading. Called effective reproduction number (Rt), it’s a variation on the much-discussed R0 (basic reproduction number) used to indicate on average how many people will catch the disease from an infected individual.

Gabriel Leung, an epidemiologist at the University of Hong Kong, says Rt is a more reliable measure than R0 because it varies according to control measures that are put in place to drive down transmission such as social distancing. R0 is an average of recorded case data, which shows previous infections rather than what’s happening now, as Rt attempts to do. Data published by his group shows that the Rt in Hong Kong has dropped to about 0.7 after hovering closer to 1 for much of March. If sustained, that would indicate the epidemic there is in decline. “It coincides with the much stricter physical distancing measures that Hong Kong has put in place,” Leung said at a media briefing in London this week.

Developing a new lifestyle with more distance is a challenge we’re going to have to face.

—Sung-il Cho, Seoul National University

Other researchers have used computer models to show that early introduction of social distancing can explain lower infection and death rates now seen in places such as China. Among the harshest restrictions in place across the world, the Chinese authorities banned people in some regions from leaving their homes, even to buy food and medicine.

Marco Ajelli, an infectious-disease expert at the Bruno Kessler Foundation in Trento, Italy, who was a member of the team that carried out the surveys in Shanghai and Wuhan, says his team’s model shows that “the social distancing measures adopted in China were sufficient to control the epidemic.” The results of other models, including one from researchers in Germany published in Science this week, support that conclusion.

Strict lockdown measures are also credited with helping Australia and New Zealand to suppress the spread of the virus so far, aided by both countries shutting their borders to international visitors early on.

There is more uncertainty over the effect of closing schools. Ajelli says his model showed that “school closures alone are not enough to contain the epidemic. Additional stricter measures, similar to those implemented in China, are needed.” Separate research from University College London also concludes that the evidence to support the closure of schools to combat COVID-19 is “very weak.”

See “Study Questions if School Closures Limit the Spread of COVID-19

As the weeks drag on, such studies are vital to determine when locked-down communities could be allowed out again—and with what restrictions. “We now have a real challenge for social distancing because people are getting really tired of it,” Sung-il Cho, an epidemiologist at Seoul National University in South Korea, said during the London briefing. “Any weakening of the social distancing could mean a new surge [in infection] because in Korea the regular lifestyle is pretty close. Developing a new lifestyle with more distance is a challenge we’re going to have to face.”

David Adam is a UK-based freelance journalist. Email him at and follow him on Twitter @davidneiladam.