Updated November 23, 2020.
As the COVID-19 pandemic continues to spread in some regions, health authorities are increasingly requiring everyone to wear masks or cloth face coverings—versus recommending or encouraging them—in indoor settings. This is because masks can be an important strategy to reduce the spread of the virus in the community, given the known spread of COVID-19 by people who are not yet (or never become) symptomatic.
Do Masks and Face Coverings Stem the Spread?
The available evidence would seem to support the widespread use of face coverings to help reduce COVID-19 transmission in the community.
A study in Health Affairs looked at the association between policies requiring the public to use masks/face coverings and the growth rate of COVID-19 in 15 states and Washington D.C. The results found a link between mask requirements and decreasing daily growth rate of COVID-19 during the period studied, April 8 to May 15, 2020. The study estimates those mask requirements possibly averted as many as 230,000–450,000 COVID-19 cases as of May 22.
In a similar study, researchers out of Texas A&M University used statistical analysis and trend projection to estimate the effect of mitigation procedures in China, Italy, and New York City. They found that using a face mask reduced the number of infections by more than 78,000 in Italy from April 6 to May 9, and by over 66,000 in New York City from April 17 to May 9.
Another systematic review published in Lancet analyzed data from 172 studies, including:
- SARS-CoV-2 (the coronavirus that causes COVID-19)
- Coronaviruses that cause severe acute respiratory syndrome (SARS) and middle east respiratory system (MERS).
According to the findings, the risk of transmission lessens with at least one meter of physical distancing, with increased protection at longer distances. The use of a mask or face covering also increased protection. As expected, N95 and other respirator masks were most effective, but cloth face coverings did have some benefit.
Findings published in the U.S. Centers for Disease Control and Prevention (CDC) Morbidity and Mortality Weekly Report may lend a real-world example in support of these findings. According to the report, two hairstylists worked while symptomatic, exposing 139 clients to COVID-19. However, both hair stylists and clients were wearing masks as required by local policy. Upon contact tracing and follow up, none of the exposed reported symptoms, and of the 67 tested, all came back negative for COVID-19. While there are limitations to applying this research (including the possibility of false negatives and missing data), the lack of spread was, in part, attributed to the mask policy.