The Science of Social Distancing

Social distancing and other nonpharmaceutical interventions (NPIs) have proven to be effective tools in most pandemics.

APRIL 1, 2020 -- Social distancing and other nonpharmaceutical interventions (NPIs) have proven to be effective tools in most pandemics. But their effect on the spread of the novel coronavirus is not yet clear, experts say.

The goal of NPIs — which include personal actions, such as staying at home when sick and washing hands, and communal ones, including school closures and canceling mass gatherings — is to flatten the height of the infection curve and build herd immunity, thus buying time to increase hospital capacity and to come up with drugs or vaccines to treat the illness.

State and local officials have been issuing stay-at-home and social distancing orders and closing schools at different times and with varying levels of restrictions.

Marc Lipsitch, DPhil, director of the Center for Communicable Disease Dynamics at the Harvard T. H. Chan School of Public Health, Boston, Massachusetts, says that social distancing is one of the only tools left to contain the spread, because the time has passed for widespread testing and contact tracing — the initial steps that could have been taken.

"I'm trying to look forward rather than back, because looking back makes me so sad," Lipsitch said during a March 25 teleconference convened by the American Public Health Association and the National Academy of Medicine.

Although social distancing has bad effects on everyone — especially the disadvantaged — it's paramount to try it, Lipsitch continued. "If we waste this time and don't do everything to build up capacity for testing, for personal protective equipment, for ventilators, for intensive care beds — all the things we know we need — it will be a further tragedy."

"There is a lot of science on this. We do know that these measures work," said Nancy Messonnier, MD, referring to NPIs during the telebriefing.

"There are enough similarities between influenza and COVID-19 to expect that we may see some of the same impact," said Messonnier, director of the Centers for Disease Control and Prevention's National Center for Immunization and Respiratory Diseases. "But it's important to look at all the layers of all of the nonpharmaceutical interventions to find out for sure that we're using the most optimal interventions at the right time."

Messonnier and Lipsitch said modeling the impact of social distancing on the coronavirus curve is a work in progress.

Lipsitch said that estimating the trigger for — and how long to maintain — social distancing depends largely on whether the novel coronavirus will follow a seasonal path like influenza viruses and other coronaviruses do.

"We don't currently know that's true for this virus," he said.

If the virus transmits at the same rate year round — that is, if it is not seasonal — a one-shot social distancing period will be effective, Lipsitch said. Under that scenario, "a modest amount of social distancing over a long period would be the best because you spread out the cases better than very intense social distancing."

But if the virus is more widespread in the winter months and wanes during warmer months, "then delaying the peak can in fact backfire," he said. In that scenario, it would be likely that more people would be infected with a one-time social distancing period than if no distancing were put in place. That "is a discouraging outcome to say the least."

He calls a one-time shot at social distancing "treacherous," but adds that "the views about seasonality are varying in the community."

Lipsitch suggests an alternative: multicycle social distancing. That is, instituting social distancing until the infection curve bends downward to a point at which it seems safe to resume social activities. Cycling such as this would result in multiple peaks but would allow for a modulation in the number of cases so that intensive care capacity would not be overstressed. If the virus declines in warmer months, on-and-off social distancing would be better, Lipsitch continued.

Other speakers noted the ongoing variability — and difficulty — of instituting social distancing in the United States.

Because the economic, political, and social costs of NPIs are high, the costs need to be carefully weighed against the severity of the circulating virus, said Howard Markel, MD, PhD, the George E. Wantz Distinguished Professor of the History of Medicine, at the University of Michigan in Ann Arbor.

For instance, school closures can create many perplexing problems, including where children go during the day if their parents are hourly wage earners with no sick leave and thus have to work, continued Markel, who is also director of the Center for the History of Medicine.

Social distancing does pose unequal burdens, said Mitch Stripling, national director of emergency preparedness and response for the Planned Parenthood Federation of America. "If the social and economic costs are too high now, society may not comply if we ask them to do this repeatedly," he said.

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