Masks protect against COVID-19. That is the conclusion of a gold-standard clinical trial in Bangladesh, which supports the findings of hundreds of previous observational and laboratory studies.first.
Critics of masked missions have cited the lack of relevant randomized clinical trials that randomly assign participants to control or intervention groups. But the latest finding is based on a randomized trial of 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 team distributed masks and promoted their use use them.
“This really should be the bottom line of the debate,” said Ashley Styczynski, an infectious disease researcher at Stanford University in California and co-author of the preprint describing the trial. Deepak Bhatt, a medical researcher at Harvard Medical School in Boston, Massachusetts who published the study on face masks, said the study “takes things a step further in terms of rigorous science.”
Styczynski and her colleagues started by developing a strategy to promote mask wearing, with measures such as reminders from healthcare workers in public places. This mask use rate eventually tripled, from just 13% in the control villages to 42% in the encouraged villages. The researchers then compared the number of COVID-19 cases in control villages and treatment communities.
The team found that the number of symptomatic cases was lower in the treatment villages than in the control villages. The reduction was modest at 9%, but the researchers suggest that the real risk reduction could be much larger, in part because they did not test for SARS-CoV-2 in people who were asymptomatic or in those who did not. have symptoms that do not meet the World Health Organization’s definition of disease.
The study linked surgical masks to an 11% reduction in risk, compared with a 5% reduction for fabric. That finding is bolstered by laboratory experiments whose results are summarized in the same preprint. According to Mushfiq Mobarak, economist at Yale University in New Haven, Connecticut, and co-author of the study. In contrast, the team found that the 3-layer cloth masks had a filtration efficiency of only 37% before washing or use.
Neither the laboratory findings nor the mask test findings were peer-reviewed.
The results of the study prompted Monica Gandhi, an infectious disease physician at the University of California, San Francisco, to switch to cloth masks. She said: “I bought myself a surgical mask – the pink one. The only other randomized clinical trial2 of the pandemic masking published to date evaluated the relationship between an individual’s infection status and self-reported mask wearing. By randomly selecting entire villages, Gandhi said, the latest research improves the assessment of both mask compliance and community-level transmission.
Face masks will remain a particularly important line of defense in Bangladesh and other low- and middle-income countries, where access to vaccines is so limited that it is non-existent. “If this changes the discourse in the US, where masks are unnecessarily politicized, that is a bonus,” said Mobarak.