Massive study finds masks work to limit COVID-19 community spread

Study involved 350,000 people in highly-populated villages

FILE - In this May 17, 2021, file photo, people walk past a sign requesting customers to wear masks in Laguna Beach, Calif. Federal health officials new, more relaxed recommendations on masks have all but eclipsed another major change in guidance from the government: Fully vaccinated Americans can largely skip getting tested for the coronavirus. (AP Photo/Jae C. Hong, File)
FILE - In this May 17, 2021, file photo, people walk past a sign requesting customers to wear masks in Laguna Beach, Calif. Federal health officials new, more relaxed recommendations on masks have all but eclipsed another major change in guidance from the government: Fully vaccinated Americans can largely skip getting tested for the coronavirus. (AP Photo/Jae C. Hong, File) (Copyright 2021 The Associated Press. All rights reserved.)

A large-scale, randomized study led by Stanford and Yale researchers found what we already knew: masks work.

The findings of the study were published this week, where researchers said they found that wearing a surgical face mask over the mouth and nose is an effective way to reduce the occurrence of COVID-19 in community settings.

About the massive masking study

The researchers enrolled nearly 350,000 people from 600 villages in rural Bangladesh.

Bangladesh is a densely populated country in South Asia. It was chosen as the site of the trial for several reasons: One, mask promotion is considered vital in countries where physical distancing can be difficult; two, Innovations for Poverty Action Bangladesh had already established a research framework in the country; and three, many local partners were eager to support a randomized, controlled trial of masking.

Those living in villages randomly assigned to a series of interventions promoting the use of surgical masks were about 11% less likely than those living in control villages to develop COVID-19, which is caused by infection with the SARS-CoV-2 virus, during the eight-week study period.

The protective effect increased to nearly 35% for people over 60 years old.

Providing free masks, informing people about the importance of covering both the mouth and nose, reminding people in-person when they were unmasked in public, and role-modeling by community leaders tripled regular mask usage compared with control villages that received no interventions, the researchers found.

In the intervention villages, they also saw a slight increase in physical distancing in public spaces, such as marketplaces. This finding indicates that mask-wearing doesn’t give a false sense of security that leads to risk-taking behaviors — a concern cited by the World Health Organization during the early days of the pandemic when its officials were considering whether to recommend universal masking.

“Our study is the first randomized controlled trial exploring whether facial masking prevents COVID-19 transmission at the community level,” said Ashley Styczynski, MD, MPH, an infectious disease fellow at Stanford. “It’s notable that even though fewer than 50% of the people in the intervention villages wore masks in public places, we still saw a significant risk reduction in symptomatic COVID-19 in these communities, particularly in elderly, more vulnerable people.”

Related: New studies reveal most people vaccinated against COVID aren’t getting seriously ill

Researchers also reported that villages with surgical masks, as opposed to cloth masks, had fewer COVID-19 cases, but said cloth masks still reduced the overall likelihood of contracting the virus.

Researchers helped villages distribute free masks to people to monitor the difference in spread before and after.

Overall, the core intervention induced 29 out of every 100 people to wear masks, increased physical distancing and reduced the number of people with symptomatic SARS-CoV-2 infections by 9 percent.

In villages that received the intervention, mask use increased by 29 percentage points (from 13 percent in the comparison villages to 42 percent in treatment villages). Mask use increased most in mosques (37 percentage points).

Map: Michigan counties with school mask mandates

“Unfortunately, much of the conversation around masking in the United States is not evidence-based,” said said Stephen Luby, MD, professor of medicine at Stanford. “Our study provides strong evidence that mask wearing can interrupt the transmission of SARS-CoV-2. It also suggests that filtration efficiency is important. This includes the fit of the mask as well as the materials from which it is made. A cloth mask is certainly better than nothing. But now might be a good time to consider upgrading to a surgical mask.”

Check out the full study here from Poverty Action.

Currently, nearly all Michigan residents are advised to wear masks indoors, regardless of vaccination status. Getting vaccinated against COVID-19 significantly decreases your risk of developing severe illness.


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About the Author:

Ken Haddad is the digital special projects manager for WDIV / ClickOnDetroit.com. He also authors the Morning Report Newsletter and various other newsletters. He's been with WDIV since 2013.