FACTS VS THE DEATH CULT:

Why aren't there more randomized studies on masks? We could have started some in early 2020, distributing masks in some towns when they weren't widely available. It's a shame we didn't. But it would have been hard and unethical to deny masks to some people once they were available to all.

Scientists routinely use other kinds of data besides randomized reviews, including lab studies, natural experiments, real-life data and observational studies. All these should be taken into account to evaluate masks.

Lab studies, many of which were done during the pandemic, show that masks, particularly N95 respirators, can block viral particles. Linsey Marr, an aerosol scientist who has long studied airborne viral transmission, told me even cloth masks that fit well and use appropriate materials can help.

Real-life data can be complicated by variables that aren't controlled for, but it's worth examining even if studying it isn't conclusive.

Japan, which emphasized wearing masks and mitigating airborne transmission, had a remarkably low death rate in 2020 even though it did not have any shutdowns and rarely tested and traced widely outside of clusters.

David Lazer, a political scientist at Northeastern University, calculated that before vaccines were available, U.S. states without mask mandates had 30 percent higher Covid death rates than those with mandates.

Perhaps the best evidence comes from natural experiments, which study how things change after an event or intervention.

Researchers at Mass General Brigham, one of Harvard's teaching hospital groups, found that in early 2020, before mask mandates were introduced, the infection rate among health care workers doubled every 3.6 days and rose to 21.3 percent. After universal masking was required, the rate stopped increasing, and then quickly declined to 11.4 percent.

In Germany, 401 regions introduced mask mandates at various times over three months in the spring of 2020. By carefully comparing otherwise similar places before and after mask mandates, researchers concluded that "face masks reduce the daily growth rate of reported infections by around 47 percent," with the effect more pronounced in large cities and among older people.

Brown, who led the Cochrane review's approval process, told me that mask mandates may not be tenable now, but he has a starkly different feeling about their effects in the first year of a pandemic.

"Mask mandates, social distancing, the other shutdowns we had in terms of even restaurants and things like that -- if places like New York City didn't do that, the number of deaths would have been much higher," he told me. "I'm very confident of that statement."

So the evidence is relatively straightforward: Consistently wearing a mask, preferably a high-quality, well-fitting one, provides protection against the coronavirus.

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