Yale study of Bangladesh shows surgical masks limit Covid spread

A study based on an enormous randomized research project in Bangladesh said that widespread wearing of surgical masks can limit the spread of coronavirus in communities.

Researchers at Yale, Stanford, the University of California Berkeley, and others was able to demonstrate what the authors said is "the effectiveness of masks in preventing infection in a real-world community setting", reports The Washington Post. 

"I think this should basically end any scientific debate about whether masks can be effective in combating covid at the population level," Jason Abaluck, an economist at Yale who helped lead the study, said in an interview, calling it "a nail in the coffin" of the arguments against masks.

The randomized trial involved more than 340,000 people in 600 villages in Bangladesh and was separated into two parts. First, researchers found that four interventions increased mask-wearing. The four interventions included no-cost free masks distribution, offering information on mask-wearing, reinforcement in-person and in public, and modeling and endorsement by trusted leaders.

Utilizing those four interventions, they found mask-wearing increased to 42% in targeted villages, up from 13% in control villages.

In the second part of the study, researchers checked those in the targeted and control villages for Covid-19 symptoms. If symptoms were reported, they were tested for Covid-19. Researchers said in villages that were targeted with mask promotion programs, there were 9.3% fewer symptomatic infections than in the control villages. If surgical masks were distributed, instead of cloth masks, infections were 11% lower overall, 23% lower among those 50-60, and 35% among people over 60.

This study contains a trio of key observations, Ranney said: One, it offers even more evidence that masks work to shield the wearer and the community. Because the research team was only able to document cases in which people were symptomatic and were seropositive for the virus, Ranney agreed that results may be an underestimate.

"To me this is the minimum effect of mask-wearing in a community," she said. "I would expect the real effect of masks is much higher, given the limitations of how they were able to measure covid in this study."

Two, it indicates that better-quality masks offer superior protection. And three, the study shows how to motivate people in a community to wear masks, by making masks a social norm.

Gostin said the research also pushed back on the "pernicious" idea that masks were only for individual protection. "[Masking is] a population-based blanket that we have to get widespread adoption of," he said.

The study does not quite claim to be the final word on masks. The authors found that while cloth masks clearly reduced symptoms, they "cannot reject" the idea that unlike surgical masks, they may have only a small effect on symptomatic coronavirus infections, and possibly none at all.

Abaluck emphasized, however, that research did not produce evidence that cloth masks are ineffective.

The results "don't necessarily show that surgical masks are much, much better than cloth masks, but we find much clearer evidence of the effectiveness in surgical masks," he said.

Abaluck also noted that the intervention group was found to practice more social distancing, which may complicate the findings on masks. However, he noted that in locations such as mosques, where many participants worshiped, there was "no physical distance," along with poor indoor ventilation — but there was increased mask-wearing.

The authors plan to conduct more research, including an evaluation of how masks limited symptomatic spread — whether by decreasing the viral load so fewer people experience symptoms, or by preventing infections entirely.

The study is under peer review with the journal Science. The authors granted journalists an early look at the results because of their potential importance in global public health debates.

Independent experts that were asked to look at the research praised its scale; some suggested that it might be the most convincing argument yet for mask-wearing.

"This is an incredibly challenging but important study to pull off," said Megan L. Ranney, an emergency medicine physician and professor at Brown University who was not involved with this research. "Anti-mask people keep saying, 'Where's the randomized controlled trial?' Well, here you go."

"It's not just modeling or looking back at studies," said Lawrence Gostin, faculty director of the O'Neill Institute for National and Global Health Law at Georgetown University, who also was not involved. "This is the gold standard of scientific knowledge."

The research is part of an ongoing project by Abaluck and his co-authors that looks not only at the efficacy of masking, but also public health methods for encouraging mask adoption among communities.

The team chose Bangladesh because co-author and Yale economist Mobarak was from the country and had worked there before, and because of increased options for funding.

Mask-wearing had been mandated in Bangladesh since March 2020, though adoption remained limited. The researchers found that they were able to increase mask-wearing in the intervention group from 13 percent to 42 percent — an increase of 28.8 percentage points. The effect was observed and found to be consistent over 10 weeks and persisted after the interventions ended.

The sheer scale of the project, which began in November and concluded in April 2021, is notable. About 178,000 Bangladeshi villagers were in an intervention group and encouraged to use masks. An additional 163,000 were in a control group, where no interventions were made.

The project assessed the levels of mask-wearing and physical distancing through direct observations from plain-clothed staff in the community at mosques, markets and other gathering places.

"This is a project that cannot be done by a handful of people," Abaluck said. "This is why there are hundreds of people involved in this project. That's why the paper has … I don't even know how many co-authors it has. Dozens of co-authors."

According to the researchers, the study opens the door to future research that should analyze expanding mask usage to fight other diseases.

"Whether people with respiratory symptoms should generally wear masks to prevent respiratory virus transmission –– including for viruses other than SARS Co-V-2 –– is an important area for future research," researchers reported in the study. "The findings from this study suggest that such a policy may benefit public health."