Measuring Masking's Protection

Environmental & Science Education, STEM, Health, Medicine, Nature of Science

Ed Hessler

The journal Nature in a daily news update refers readers to a medRxiv preprint (Medical Archives) which has not yet been peer reviewed. It asks where/when to face masks as a COVID-19 preventative matter most.

 "Rxivs" have proliferated in the last few years. They provide results to others and also used for feedback on the studies. It is a great practice, one I appreciate. 

The researchers analyzed hundreds of COVID-19 cases and found, not surprisingly, but how good it is to have evidence, masks matter most during long encounters and indoors. It is not a small study--more than a thousand people who had tested positive for SARS-CoV-2. And the circumstances are quite specific. Each infected participant was matched with at least one control person with matching factors, e.g., age and sex, but who tested negative during the same time period. Indoors matters as do encounters that lasted for more than three hours.

"Participants exposed to someone with COVID-19 had lower odds of infection if masks were worn at the encounter than if they weren't." (emphasis mine)

The news item is brief but has more details, including criticisms, e.g., size of benefits, "precise figures on masking's benefits, and the challenge of matching infected people with controls. However, one of the critics, biostatistcian Grant Brown, notes that "even so, (the study is) a reasonable approach to a hard problem."

h/t Nature Briefing November 4, 2021