A massive new study conducted in Bangladesh released Tuesday seemingly provides strong evidence that community-wide masking stops the spread of COVID-19, but with a few important caveats.
The study, conducted primarily by researchers from Yale and Stanford, found that a 29% increase in mask-wearing in Bangladeshi villages led to a 1% decrease in incidence of COVID-19 symptoms. The reduction was stronger when using surgical masks than cloth masks, and was particularly pronounced in the elderly.
The resource-intensive study was the first of its kind conducted during the pandemic. Researchers designated 300 intervention villages and 300 comparison villages in rural and peri-urban Bangladesh. In the intervention villages, they distributed free masks, offered information on masking benefits, had local religious leaders and community members encourage mask-wearing, offered incentives for high masking-rates and implemented public reminders and nudges to wear masks via mediums like signage and text messages.
Those interventions resulted in the 29-point increase in masking rate in the intervention villages compared to the comparison villages, from 13% to 42%. (RELATED: ‘Natural Immunity Is Really Better’: New Israeli Study Fuels Debate On Vaccination Versus Natural Immunity)
Another data point that catches attention, though, is that the mask-wearing did virtually nothing for anyone under 50 years old. In villages that used surgical masks, COVID-19 prevalence in people aged 60 and over fell from 1.03% to 0.69%, a relative decrease of 34.7%. Ages 50-60 saw a relative drop of 23%. Below age 50, however, researchers found no statistically significant decrease in COVID-19 seroprevalence.
The data suggests that the elderly benefit from community masking, and the elderly are at the greatest risk from COVID-19. But while the results were statistically significant, they were fairly limited. The study found just a 0.7% absolute decrease in COVID-19 symptoms in the cloth mask villages, and a 1.1% absolute decrease in the surgical mask villages.
Question for Jason and Katy — How do you tease out effects of masking vs. behavior change that comes with wearing a mask? (E.g., you have a mask on, you think more about COVID-19, you become more cautious.)
— Brad Stulberg (@BStulberg) September 1, 2021
Another factor is that increased mask-wearing wasn’t the only change that occurred. The study found that the intervention villages increased social distancing, despite the researchers making no efforts to encourage social distancing in the population. The increase in social distancing was higher in the villages that got surgical masks compared to cloth masks, which were coincidentally the same villages that saw better results.
Let me follow up why this may be relevant – the increase in physical distancing was actually larger in villages where surgical masks were distributed.
So the larger effect you find for surgical masks may be partly driven by a larger increase in physical distancing in these places pic.twitter.com/Gjc6iLmJqL
— Piotr Lewandowski (@ptrlewandowski) September 1, 2021
Rural Bangladesh is also a very different environment than many developed countries in a key way when it comes to virus mitigation strategies. Only four percent of Bangladesh was vaccinated as of Aug. 21. In the U.S., 62% of the total population has received one dose, and 52.4% are fully vaccinated. More than 70% of adults are at least partially vaccinated. As vaccination remains by far the strongest preventative tool against COVID-19 infection, symptoms and death, it’s unclear whether the benefits of community masking presented in the Bangladesh study would appear as strongly in communities with high vaccination rates.
The study also provided no insight into the question of masking for children. Children under age 12 remain the only population in the U.S. unable to get vaccinated, and whether or not to mandate masks in schools is the primary debate happening currently with regard to masking. The data suggests that masking kids may marginally benefit the adults around them, who have by now chosen whether or not to get vaccinated, but says nothing as to whether masking will benefit the kids themselves in a significant way.
Odd that mask advocates are excited by this study. As a vaccine advocate, I would be horrified if a vaccine trial showed 11% efficacy. Based on the 95% confidence intervals, we do not even know if surgical mask efficacy is more than 0%. https://t.co/N7d5bjbxxe
— Martin Kulldorff (@MartinKulldorff) September 1, 2021
Critics of the study also pointed out that, based on the 95% confidence intervals reported, it’s possible the cloth masks had zero effect. (RELATED: Two Top Vaccine Officials Resign From FDA Amid Political Pressure From Biden Administration)
The study shows that community masking helps slow the spread of COVID-19 by a relatively small amount among the elderly in a community with little-to-no vaccinated people. In the U.S., where most adults are vaccinated, and the most vulnerable were prioritized for vaccination and other mitigation efforts are available (ventilation, more advanced medical care, etc.), the meaning is less clear.