FANCY THAT:

This week, a group of scientists from Yale, Stanford, UC Berkeley, and other institutions published the final results of a randomized study of community-wide masking behavior in Bangladesh. The study encompassed roughly 350,000 people in 600 villages. The researchers randomly selected certain villages for an intervention that included giving out free masks, paying villagers to remind people to cover their face, and having village leaders and religious figures such as imams emphasize the importance of masks. The researchers also paid villagers to count properly worn masks in public places, including markets and mosques. To gather data on coronavirus transmission, the team asked about symptoms and conducted blood tests to determine who came down with COVID-19 over the course of the study.

Their conclusion? Masks work, period. Surgical masks are particularly effective at preventing coronavirus transmission. And community-wide mask wearing is excellent at protecting older people, who are at much higher risk of severe illness from COVID-19.

To some, this conclusion might sound like the work of liberal conspiracists to permanently swaddle our faces in tyrannical cloth. To others, it might sound like very old news. After all, you might think, if people were masking successfully during the 1918 flu pandemic, why do we need a 2021 study to prove the benefits of the practice? But the Bangladesh study is still perhaps the most important research done during the pandemic outside of the vaccine clinical trials, because it gives us randomized-trial data to bolster the flimsier assumptions and conclusions of observational research. We finally have a sense of not just whether masks work but how much universal masking could reduce transmission. The answer is: quite a lot.

The randomly assigned pro-masking policy reduced the number of confirmed, symptomatic COVID-19 cases in the intervention group by nearly 10 percent, relative to the control group. That might not sound like a huge effect. But the intervention increased masking from 14 percent to only 43 percent; 100 percent masking would have likely had a much larger effect.

Even more impressively, the villages that implemented pro-masking policies saw a 34 percent decline in COVID-19 among seniors, for whom the disease is most deadly. This could be because older villagers are more likely to properly wear masks, or because they are more likely to have symptomatic infections if they come into contact with the coronavirus.

The study also found clear evidence that surgical masks are better at reducing the spread of symptomatic COVID-19 than cloth masks. In focus groups, Bangladeshi participants said they preferred cloth masks because they seemed to be more durable. But the researchers found that, on the one hand, surgical masks were more efficient, even after being washed 10 times with soap and water. "On the other hand, we found only mixed evidence about cloth masks," Jason Abaluck, a co-author of the study and a professor at Yale, told me. People wearing cloth masks had fewer symptoms, such as coughs, than the control group, which suggests some effect. But cloth-mask wearers didn't have significantly fewer coronavirus antibodies as determined by blood tests. "We cannot reject that [cloth masks] have zero or only a small impact on symptomatic SARS-CoV-2 infections," Abaluck wrote along with Mushfiq Mobarak of Yale, Laura Kwong of UC Berkeley, Stephen Luby and Ashley Styczynski of Stanford, and other researchers.

Creating a social norm is hard work. The pro-masking intervention in this study was aggressive, extensive, and expensive. In all, the researchers distributed more than 1 million masks. Free distribution of masks was important. But of all the interventions, mask promotion--that is, paying individuals to remind people on the street to cover their face--seemed to have the biggest effect. "Reminders from people in the village almost acted as booster shots for masking," Abaluck told me. The research team is currently working on scaling up its intervention in countries including Pakistan, India, and Nepal.

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