The New Yorker:

On Wednesday evening, Eric Garcetti, the mayor of Los Angeles, gave the people of his city a message regarding masks: if you really must go out on the street, for whatever reason, cover your mouth and nose. But don’t go out and buy N95 or surgical masks. Medical workers in hospitals thick with COVID-19 cases need those, and there are not enough even for them. For everyone else, a cloth mask, home-sewn or rigged up, or even a “tucked-in bandanna,” combined with social distancing, would at least be a start. “We’re going to have to get used to seeing each other like this,” Garcetti said. “This will be the look.” He told people in the city to post images of themselves wearing masks on social media with the hashtag #LAPROTECTS.

There is much that remains uncertain in the epidemiology of the novel coronavirus. The best reason for wearing even non-N95 face masks, as the science writer Ed Yong noted in a summary of the evidence in The Atlantic, is not that they will absolutely shield you from the virus—they probably won’t—but that “they can stop viruses from getting out.” In other words, masks prevent their wearers from spreading virus-bearing droplets. Los Angeles was ahead of New York City in closing schools; Garcetti’s advice sounds like something else that should probably have been issued here and in other hard-hit areas already. The reasoning was clear even in what were, as of Thursday, the Centers for Disease Control and Prevention’s hedged directives regarding masks. Currently, they say that “a facemask should be used by people who have COVID-19 and are showing symptoms. This is to protect others from the risk of getting infected.” But there is growing, strong evidence of asymptomatic and presymptomatic transmission of the virus. So how do you know if you have COVID-19, in the absence of testing? The C.D.C. has said that it is considering issuing even stronger guidance on masks and face coverings, but, logically, it’s there already.

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