By Dr. Laura (Layla) H. Kwong, PhD, University of California, Berkeley — The Conversation — 22 September 2021
The largest randomized controlled trial to date on mask-wearing — conducted from November 2020 to April 2021 in rural Bangladesh, involving 341,126 adults in 600 villages — has provided gold-standard evidence that wearing masks, particularly surgical masks, prevents COVID-19. In 300 villages masks were not promoted; in 200 villages surgical masks were distributed and promoted; in 100 villages cloth masks were promoted. Mask usage more than tripled in the mask groups, from 13% to 42%, and physical distancing also increased by 5%. In villages where any type of mask was distributed, COVID-19 fell by 9% compared to non-mask villages. In villages where surgical masks specifically were distributed, COVID-19 fell by 12% — and by 35% for people aged 60 and over, and 23% for those aged 50–60.
The study was led by Dr. Laura (Layla) H. Kwong in close collaboration with researchers from Yale, MIT, and the University of California, and partners in the Bangladeshi government. Together with prior laboratory and observational evidence — including a late-2020 study of 196 countries finding that countries with mask-wearing cultural norms or policies saw weekly per-capita COVID-19 mortality increase 16% during outbreaks versus 62% in countries without such norms — the body of evidence strongly supports mask-wearing. “Cloth masks are likely better than nothing, but high-quality surgical masks or masks with even higher filtration efficiency and better fit — such as KF94s, KN95s and N95s — are the most effective at preventing COVID-19,” Dr. Kwong concluded. “Given that COVID-19 can so easily spread from person to person, if more people wear masks the benefits increase.”