What Does the Research Say?
A large-scale, real-world study published this month found surgical masks especially effective at reducing symptomatic infections. These types of masks prevented 1 in 3 infections among people 60 and older.
Researchers from Yale, Stanford and the nonprofit GreenVoice monitored more than 340,000 adults in rural Bangladesh for at least eight weeks. Roughly half the Bangladeshis received interventions like free mask distribution and promotion. Villages that received interventions saw mask use jump from 13% to 42%. The same villages reported fewer confirmed covid infections and a lower incidence of related symptoms.
Villages where cloth masks were given out reported an 8.5% reduction in symptoms, while villages that received surgical masks reported a 13.6% reduction. When a third of adults with symptoms commonly associated with covid agreed to get their blood tested for the virus, researchers discovered an 11% reduction among those who wore surgical masks. Researchers observed a 5% reduction in infections among those who wore cloth masks. This study was conducted before the delta variant was circulating widely in the country. The study has not yet undergone peer review, but some experts have already heralded its methodology and results.
“When I saw those results, I threw away my cloth mask,” said Stephen Luby, a co-author of the study and professor of infectious disease at Stanford University. “If delta is circulating and if you’re going to wear a mask, why don’t you wear one that the data tell you is good?”
“We find very strong evidence that surgical masks are effective,” added Jason Abaluck, an economist at Yale who helped lead the study. “My read of that is that cloth masks are probably somewhat effective. They are probably better than nothing.”
Abaluck suspects his study offers mixed evidence for cloth masks because only about a third of those who reported symptoms consented to blood testing for covid. In other words, the sample size was too small to observe anything significant. “The most likely interpretation of this whole constellation of results is that [cloth masks] actually do help. They actually do make you less likely to get covid. That’s why we saw fewer symptoms,” he said. A second possibility is that cloth masks prevent other respiratory diseases that have similar symptoms, he said.
Multiple observational studies and trend analyses found community masking, which includes the use of cloth masks, reduces the spread of covid. The researchers of the Bangladesh study said those studies had drawbacks, which is why they conducted a randomized clinical trial. For example, some of those studies could not observe the independent effect of masks in real-world settings because they looked at the aftermath of mask mandates, which were often coupled with other covid mitigation steps such as physical distancing. However, they agreed with those studies’ overall assessment: People who wear masks are less likely to get infected than people who don’t.
“This is the nature of science. Science evolves,” Luby said. “We had evidence that we get some protection from cloth masks, and we now have newer evidence that we get better protection from surgical masks.”