First randomized trial on masking affirms efficacy, Yale study says
The effectiveness of masks in preventing COVID-19 has been supported by the results of a 300,000-person randomized trial in Bangladesh led by two School of Management researchers.
Courtesy of Innovations for Poverty Action
A new study coauthored by two Yale School of Management researchers affirmed that mask wearing reduced the spread of COVID-19 and that surgical masks, rather than cloth masks, were more effective in that reduction. The 300,000-person study was the first randomized trial on mask efficacy.
Yale professors of economics Ahmed Mushfiq Mobarak and Jason Abaluck, alongside a team of researchers from Stanford University and the University of California at Berkeley, conducted a cluster-randomized trial in rural Bangladesh that tested the intervention of community-level masking promotion from November 2020 to April 2021. The intervention reduced symptomatic seroprevalence — the presence of COVID-19 antibodies in the population — by 9.3 percent overall, 11.2 percent when surgical masks were used and more than 20 percent for individuals in the sample over the age of 50.
“Our study was organized in order to address two essential goals,” Mobarak said. “First, to identify strategies for us to consistently increase mask wearing in low- [and] middle-income countries, with Bangladesh being a representative example, and, second, to assess the impact of the initiative to increase mask wearing on symptomatic SARS-CoV-2 infections.”
The study included 600 Bangladeshi villages and a total of 342,126 adults — 178,288 individuals in the treatment group and 163,838 in the control group, according to the paper. The intervention group was given free masks, information on the importance of masking, role modeling by community leaders and regular in-person reminders for eight weeks. The control group did not receive any interventions.
The researchers randomly assigned the different villages to the treatment versus control groups. Within the former group, they further randomized which villages would be given cloth masks as opposed to surgical ones, the paper explained.
Mask wearing and physical distancing were assessed through weekly direct observation at high-traffic public locations. At five-week and nine-week follow ups, reachable participants were surveyed about COVID-19 symptoms as defined by the World Health Organization, according to the paper.
Mobarak, who is originally from Bangladesh, said the trial was conducted there to “continue a long standing tradition of Bangladesh teaching the world about how to improve health outcomes, especially among rural poor populations, in a cost-effective way.”
Mobarak also cited the abilities to carry out high-volume data collection, mask manufacturing, blood sampling and COVID-19 testing in Bangladesh as additional motivators for conducting the trial in Bangladesh.
By the end of the study period, the researchers found that the promotion of masks increased proper mask wearing to 42.3 percent in the treatment villages, compared to 13.3 percent in control villages. This tripling of mask usage was sustained during the intervention period and for two weeks after, according to the paper. The impact of the intervention dropped to 26 percent after five months — the duration of the study — but remained 10 percentage points higher in the intervention group. The treatment also reduced symptomatic seroprevalence by 9.3 percent overall, with villages randomized to surgical masks showing a relative reduction of 11.2 percent.
“A lot of conversation around mask usage previously had been that there had never been a randomized, controlled trial that demonstrated that masks were effective in both interrupting and preventing disease,” said Stephen Luby, professor of infectious diseases at Stanford University and a coauthor of the study. “This really was a gold standard trial and was able to demonstrate just that.”
In addition to seeing a widespread effect of the implementation, the elderly were a particular subgroup that experienced a higher reduction of symptomatic seroprevalence with surgical masks — 23 percent for individuals ages 50 to 60 and 35 percent for those over 60. The higher reduction may be due to the elderly having smaller social networks, or simply because mask wearing lowered viral loads under the threshold that is susceptible to transmission in older subgroups, Abaluck said.
To conduct a study of this magnitude, researchers said that coordination between a variety of research specialties was especially important.
“It’s been a truly interdisciplinary project,” Laura Kwong, an assistant professor in environmental health sciences at UC Berkeley and fellow coauthor, said. “We were able to reach across fields to work with other professionals to really create something much bigger than one could create alone. It’s been great to have economists, public health specialists, engineers, behavioral scientists and biostatisticians, among others, collaborating on this effort.”
Moving forward, this research group is working to expand upon their work.
According to Abaluck, they are planning to conduct a close replication of the original study in order to test the effectiveness of masking against the delta variant and asymptomatic transmission.
“Our goal in the next couple of months is to reach around 100 million people,” Abaluck said. “But we hope to do even more than that. We are working on scaling up while maintaining some fidelity of the original intervention.”
His team is currently working with others to expand this study throughout South Asia and then to other parts of the world.
Given the study’s findings on the importance of masking, it is important to focus on using it in conjunction with other public health tools, according to Sydney Jones, a senior technical advisor in epidemiology at the global public health organization Vital Strategies.
“We need to use the tools available together,” Jones said. “We have the tool of vaccines. It’s vital that we vaccinate as many people as possible. But, we also have masking, social distancing and avoiding crowded spaces. We should be using all of these in a complementary way to try and prevent the spread of COVID-19.”
Yale University requires all individuals, regardless of vaccination status, to wear masks indoors while on campus.