We Did the Research: Masks Work, and You Should Choose a Surgical Mask if Possible

Masks, especially surgical ones, substantially reduce the risk of getting Covid-19. Getting more people to wear them — through mandates or strategies like handing out masks at churches and other public events — could save thousands of lives each day globally and hundreds each day in the United States.

While this may seem like common sense more than 18 months into the pandemic, early studies on masking had raised important questions. Mask mandates appeared to reduce Covid-19 cases, but was this because of masking, or because people in places with mask mandates would have become more careful even without them? Because of this uncertainty, some governments and public health agencies were hesitant to recommend them. That’s why we ran one of the largest and most sophisticated studies of mask wearing, using the “gold standard” of research design, a randomized controlled trial, to evaluate whether communities where more people wear masks have fewer cases of Covid-19.

Many people live in countries where vaccines are not yet widely available. Even in the United States, vaccines are available but used unevenly, and the weekly death rate from Covid-19 remains high. In both of these environments, masks are a critical and inexpensive tool in the fight against the coronavirus.

Our research, which is currently undergoing peer review, was conducted with 340,000 adults in 600 villages in Bangladesh and tested many different strategies to get people to wear masks.

Our research team settled on distributing masks directly to people’s homes and in crowded public places like mosques and markets. We provided information on why mask wearing was important, and involved religious and community leaders in that messaging. Finally, we had residents in each village politely ask anyone not wearing a mask to put one on, and give masks to whoever needed one.

While not everyone agreed to mask up, mask wearing increased by about 30 percentage points among the adults who were encouraged to do so. This change led to a 9 percent reduction in Covid-19 overall. In communities where we promoted surgical mask use, Covid-19 cases dropped by 11 percent.

Our study did not measure the effect of universal mask wearing but the effect of a voluntary mask program. It resulted in an increase to four in 10 people using a mask from one in 10 people masking — a large rise in use, but still far from perfect. If everyone wore masks, the reductions in Covid-19 cases would most likely have been substantially larger.

People over age 50 benefited most, especially in communities where we distributed surgical masks. In these communities, Covid-19 cases fell by 23 percent for people aged 50 to 60 and by 35 percent for people over age 60. Our study does not suggest that only older people need to wear masks, but rather that widespread community mask wearing reduces Covid-19 risk, especially for older people.

Let us put this in concrete terms. Our best estimate is that every 600 people who wear surgical masks in public areas prevent an average of one death per year given recent death rates in the United States. Think of a church with 600 members. If a congregation learned that it could save the life of a member, would everyone agree to wear surgical masks in indoor, public areas for the next year?

We also tested the filtration of surgical masks that had been worn, crumpled up in pockets and purses, and washed with soap and water up to 10 times. These masks still prevented more virus particles from passing through than typical cloth masks. Masks with even better filtration or fit than surgical masks, such as KF94 or KN95 masks, may provide even stronger protection than surgical masks if worn properly.

The bottom line is masks work, and higher quality masks most likely work better at preventing Covid-19. If you have the ability to choose between a cloth and a surgical mask, go with surgical. But the best mask is one that a person will actually wear and wear correctly.

Mask wearing need not be permanent. More surgical masks in high-risk areas today can mean less need for masks tomorrow, preventing many deaths along the way. In places where mask mandates are not feasible or possible, softer alternatives — like a greeter handing out masks at a mall entrance — can be remarkably effective. Our research suggests that if handed a mask and asked politely to please wear one, many people will do so. Not everyone will, but not everyone needs to for lives to be saved.

Mr. Abaluck is a professor of economics at the Yale University School of Management. Ms. Kwong is an assistant professor in environmental health sciences at the University of California, Berkeley School of Public Health. Dr. Luby is a professor of medicine in the infectious diseases division at Stanford University.

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