March 26, 2020

Yes, social distancing really works. Here's how the 1918 flu epidemic proves it.

Daily Briefing

    Some public officials, including President Trump, have expressed a desire to end social distancing practices sooner rather than later, but studies of the 1918 Spanish flu epidemic show that easing social distancing efforts related to the new coronavirus too early could lead to a spike in deaths.

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    Some officials call to end social distancing measures soon

    In an effort to stem the spread of the new coronavirus, many states and localities have implemented social distancing measures, including closing all non-essential businesses and restricting bars and dining establishments to carry-out and delivery only. Trump this week indicated he wants U.S. businesses to reopen by April 12, saying continued closures eventually could threaten Americans more than the country's COVID-19 epidemic.

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    "We can't have the cure be worse than the problem," Trump said, adding, "We have to open our country because that causes problems that, in my opinion, could be far bigger problems." Trump went on to say that, if U.S. businesses stay closed for months, there "probably [would be] more death from that than anything that we're talking about with respect to the virus."

    However, Trump during a White House press briefing on Tuesday clarified that any "decision" on the matter "will be based on hard facts and data."

    How the 1918 Spanish Flu epidemic proves social distancing works

    Trump isn't the first official to raise concerns about the economic effects of social distancing. During the 1918 Spanish flu epidemic, many cities in the United States expressed similar concerns, worrying that social distancing measures could harm the economy, Vox reports.

    St. Louis, for instance, elected to reduce its Spanish flu social distancing measures early, and a 2007 study published in JAMA found that doing so led to a spike in deaths, with the death rate falling only after the social distancing measures were implemented again.

    Several other cities had a similar experience, the study found.

    Howard Markel, director of the University of Michigan's Center for the History of Medicine and an author on the study, said the results of reducing measures early looked like a bunch of "double-humped epi curves." Flu cases dropped when social distancing measures were implemented, spiked when the measures were removed, and fell again when the measures were implemented again.

    The study found that a second spike in deaths only occurred in cities that pulled back their social distancing measures. "Among the 43 cities [in the study], we found no example of a city that had a second peak of influenza while the first set of nonpharmaceutical interventions were still in effect," the authors of the study wrote.

    Another Spanish flu study, published in PNAS in 2007, found similar results. "[N]o city in our analysis experienced a second wave while its main battery of [nonpharmaceutical interventions] was in place. Second waves occurred only after the relaxation of interventions," the authors wrote.

    The study also found that, on the whole, social distancing measures were effective, especially when implemented early on.

    "Consistent with this hypothesis, cities in which multiple interventions were implemented at an early phase of the epidemic had peak death rates ≈50% lower than those that did not and had less-steep epidemic curves," the authors wrote. "Cities in which multiple interventions were implemented at an early phase of the epidemic also showed a trend toward lower cumulative excess mortality, but the difference was smaller (≈20%) and less statistically significant than that for peak death rates."

    The study concluded that cities that experience a severe infectious disease outbreak for which there is no sufficient vaccine supply would "likely need to maintain [nonpharmaceutical interventions] for longer than the two to eight weeks that was the norm in 1918."

    In short, when interventions like social distancing work, it can be difficult for the public to notice, because they won't be able to see prevented deaths, Vox reports. Tara Smith, an epidemiologist at Kent State University, said, "It's the paradox of public health: When you do it right, nothing happens" (Lopez [1], Vox, 3/24; Lopez [2], Vox, 3/24).

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