Here's How Much a Mask Reduces Coronavirus Transmission

A first-of-its-kind study using data from 16 countries on six continents offers some of the first evidence that face masks and physical distancing really do prevent the spread of COVID-19. The findings published in the Lancet—based on studies of 25,000 patients with COVID-19 or the coronaviruses SARS and MERS, per the CBC—don't come as a surprise but they do eliminate some "uncertainty," study co-author Derek Chu tells Today. Researchers at Canada's McMaster University found one's risk of transmitting a coronavirus without preventive measures was 17.4%. With a mask or respirator, it fell to 3.1%. The study also found "physical distancing is highly effective, and every inch counts," Chu tells Today.

The risk of transmission at less than a meter (a little over three feet) of distance without other forms of protection was 12.8%. At more than a meter, it was 2.6%. Chu notes seven feet, or more than two meters, is probably ideal. Researchers also identified a 16% transmission risk for those who did not wear eye protection; this dropped to 5.5% for those who wore a face shield or goggles. "Having that barrier would help prevent our hands touching our eyes, and it's also a barrier against the virus," Chu said. Still, he stresses the importance of hand washing as "no single intervention on its own made an individual completely impervious to transmission." A press release points out some of the study's limitations. Among them: "Few studies assessed the effect of interventions in non-healthcare settings, and most evidence came from studies of SARS and MERS." (Here's the latest on a vaccine.)