In the first weeks of the COVID-19 pandemic, health authorities advised against the use of masks by the public, concerned about diverting supplies from healthcare workers and creating a false sense of security that would reduce compliance with public health recommendations like social distancing and hand washing. By April 2020, the U.S. Centers for Disease Control had reversed itself; in June, the World Health Organization followed suit. Masks were eventually adopted in much of the world. But evidence of the effectiveness of masks in preventing infection has been limited to lab experiments and healthcare settings.
Now, for the first time, a randomized trial has demonstrated the effectiveness of masks in preventing infection in a real-world community setting. A large study in Bangladesh, co-authored by Yale SOM’s Jason Abaluck and Mushfiq Mobarak, found that a campaign to promote mask-wearing reduced symptomatic infections significantly, particularly among older people and those using surgical masks.