An enormous randomized trial of communities in Bangladesh seems to provide the clearest evidence yet that regular mask-wearing can impede the spread of the covid-19 pandemic. The study found that villages where masks were highly promoted and became more popular experienced noticeably lower rates of covid-like symptoms and confirmed past infections than villages where mask-wearing remained low. These improvements were even more pronounced for villages given free surgical masks over cloth masks.
Plenty of data has emerged over the last year and a half to support the use of masks during the covid-19 pandemic, both in the real world and in the lab. But it’s less clear exactly how much of a benefit these masks can provide wearers (and their communities), and there are at least some studies that have been inconclusive in showing a noticeable benefit.
Last late year, however, dozens of scientists teamed up with public health advocacy organizations and the Bangladesh government to conduct a massive randomized trial of masks—often seen as the gold standard of evidence. And on Wednesday, they released the results of their research in a working paper through the research nonprofit Innovations for Poverty Action.
The study involved 600 villages in a single region of the country with over 350,000 adult residents combined. Similarly matched villages were randomly assigned to two conditions (a pair of villages with similar population density, for instance, would go to one condition or the other). In one condition, the researchers and their partners promoted the use of masks through various incentives between November 2020 and January 2021. These incentives included free masks, endorsements by local leaders, and sometimes financial prizes for villages that achieved widespread mask usage. In two-thirds of the intervention villages, the free masks given were surgical, while one-third were given free cloth masks. In the second condition, the researchers simply observed the villages and did nothing to encourage masks during that time.
Residents in the villages where masks were encouraged did start wearing them more, though no individual nudge or incentive seemed to do better than the others. By the end, about 42% of residents in these villages wore masks regularly, compared to 13% of those in the control group. And in these communities, the odds of people reporting symptoms that may have been covid or testing positive for antibodies to the virus declined.
Overall, the average proportion of people who reported symptoms in the weeks following the mask promotions went down by 11% in these villages compared to the control group, and the average number of people having antibodies went down by over 9%. These differences were larger for surgical mask-wearing villages (12% vs 5% for reducing symptoms) and for residents over 60 (35% for reducing infections for older residents in surgical mask-wearing villages).
Some of this effect might not have come directly from the ability of masks to block transmission of the virus. Those who used masks, the study found, were also more likely to practice social distancing. That’s a relevant finding, the authors note, since some people who have argued against mask mandates do so by claiming that masks will only make people act more carelessly. This study suggests that the opposite is true—that masks make us more, not less, conscientious of others.
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