The study, published in Science and titled “The Impact of Community Masking on COVID-19: A Cluster-Randomized Trial in Bangladesh,” was the first large-scale randomized trial to demonstrate the effectiveness of masks in preventing COVID-19 in a community setting. It found that a campaign to promote mask-wearing in Bangladesh reduced symptomatic infections significantly, particularly among older people and those using surgical masks. A collaboration with the research and policy group Innovations for Poverty Action, it was co-authored by scholars from Stanford University, the University of California Berkeley, and other universities.
In the new publication, which replaces interim guidance issued in December 2020, the WHO recommends the use of medical masks or non-medical masks that meet WHO guidelines for the general public when interacting with people outside their households in settings with community or cluster transmission of COVID-19. In contrast with the interim guidance, the new publication discourages the use of homemade and other non-medical masks that don’t meet WHO guidelines unless the preferred masks are not available.
The publication cites various studies in support of the recommendation, including the Yale SOM study. “A cluster randomized controlled trial evaluating mask promotion (as an indirect public health intervention) found that in a country with low mask use, mask promotion increased mask use and decreased symptomatic SARS-CoV-2 seroprevalence,” it reads.