Ed note: A surgical mask is a loose-fitting, disposable device that creates a physical barrier between the mouth and nose of the wearer and potential contaminants in the immediate environment. These are often referred to as face masks, although not all face masks are regulated as surgical masks. Note that the edges of the mask are not designed to form a seal around the nose and mouth. As the study below confirms, the surgical mask is much better than a cloth mask.
From Mike C.
A gold-standard clinical trial has concluded that wearing masks reduces the spread of COVID-19, backing up the findings of hundreds of previous observational and laboratory studies.
Critics of mask mandates have cited the lack of relevant randomized clinical trials, which assign participants at random to either a control group or an intervention group. But the latest finding is based on a randomized trial involving nearly 350,000 people across rural Bangladesh. The study’s authors found that surgical masks — but not cloth masks — reduced transmission of SARS-CoV-2 in villages where the research team distributed face masks and promoted their use (J. Abaluck et al. Innovations for Poverty Action Working Paper https://go-nature-com.libproxy.lib.unc.edu/3hhfeki; 2021).
“This really should be the end of the debate,” says study co-author Ashley Styczynski, an infectious-disease researcher at Stanford University in California.
Styczynski and her colleagues began by developing a strategy to promote mask wearing, with measures such as reminders from health workers in public places. This ultimately tripled mask usage, from only 13% in control villages to 42% in villages where it was encouraged. The researchers then compared numbers of COVID-19 cases in the control villages and the treatment communities.
The team found that the number of symptomatic cases was lower in treatment villages than in control villages. The decrease was a modest 9%, but the researchers suggest that the true risk reduction is probably much greater, in part because they did no SARS-CoV-2 testing of people who had no symptoms or whose symptoms did not meet the World Health Organization’s definition of the disease.
The study linked surgical masks with an 11% drop in risk, compared with a 5% drop for cloth masks. That finding was reinforced by laboratory experiments, which showed that even after 10 washes, surgical masks filter out 76% of small particles capable of airborne transmission of SARS-CoV-2. By contrast, the team found that 3-layered cloth masks had a filtration efficiency of only 37% before washing or use.
Nature 597, 309 (2021)