The researchers estimate that among a group of Bangladeshi adults in the study that were encouraged to wear masks, mask-wearing increased by 28.8 percent after the intervention. When tracked, this group saw a 9.3 percent reduction in symptomatic covid-19 seroprevalence, meaning the virus was confirmed by bloodwork, as well as a further 11.9 percent reduction in covid-19 symptoms.
The study’s authors — led by principal investigators Abaluck, Laura Kwong, Steve Luby, Ahmed Mushfiq Mobarak and Ashley Styczynski — a globe-spanning team that includes researchers from Yale, Stanford and the Bangladeshi nonprofit GreenVoice, emphasized that this did not mean masks were only 9.3 percent effective.
“I think a big error would be to read this study and to say, ‘Oh, masks can only prevent 10 percent of symptomatic infections,’ ” Abaluck said. The number would probably be several times higher if masking were universal, he said.
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.
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.
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