Wearing a surgical face mask over the mouth and nose reduces the spread of Covid-19 in community settings, according to a new study based on real-life evidence. The researchers also found that targeted actions to promote mark-wearing can significantly increase their use, especially in rural and low-income countries.

The study, which has not been peer-reviewed yet, is the largest randomized trial so far to demonstrate how effective surgical masks are to reduce the spread of the coronavirus. While previous work was often done on hospitals and laboratories, the new findings show the efficacy of masks in the real world and on a really massive scale. 

Researchers from Bangladesh and the United States tested the effectiveness of surgical masks across 600 villages in Bangladesh and with more than 342,000 adults. After their program ended, encouraging people to use masks, they found an 11.9% decrease in symptomatic Covid-19 symptoms and a 9.3% drop in symptomatic seroprevalence 

“We now have evidence from a randomized, controlled trial that mask promotion increases the use of face coverings and prevents the spread of COVID-19,” Stephen Luby, one of the authors, said in a statement. “Importantly, this approach was designed to be scalable in lower- and middle-income countries struggling to get or distribute vaccines.”

Tracking the use of masks

The researchers randomly selected villages in Bangladesh to implement programs to encourage the use of face masks. They handed over free surgical masks, offered information about their importance, and reinforced their overall use in the community. Thanks to this, mask-wearing rose by 30% and the change of behavior lasted for 10 weeks or more.

Wearing face masks more than before didn’t give people a false sense of security that leads to risk-taking behaviors, the findings showed. This used to be a concern during the early days of the pandemic by the World Health Organization. The researchers also reported an increase in physical distancing in public spaces thanks to their campaigns to encourage the use of masks. 

“We saw an opportunity to better understand the effect of masks, which can be a very important way for people in low-resource areas to protect themselves while they wait for vaccines,” Laura Kwong, one of the study’s co-authors, said in a statement. “So we collaborated with behavioral scientists, economists, public health experts and religious figures.” 

The researchers specifically chose Bangladesh, a highly populated country in South Asia, for specific reasons. Encouraging the use of masks is essential in countries where physical distances can be tricky. Plus, there was already a research framework in the country and local researchers were eager to do a controlled trial of masking. 

Despite plenty of evidence over the important role of masks to avoid the spread of the virus, it’s been tricky to increase mask-wearing in many countries, especially those low-resource ones such as Bangladesh. In July 2020, one-fifth of Bangladeshis wore a mask that covered mouth and nose in public areas, despite a nationwide mask mandate. 

The findings have big implications for countries that rely on mitigation measures to slow the spread of the virus until they get better access to vaccines, the researchers argued. But there are lessons also applicable for countries with plenty of vaccines, such as the US, where some cities starting to enforce the use of face-mask due to the delta variant. 

“Our study provides strong evidence that mask wearing can interrupt the transmission of SARS-CoV-2. It also suggests that filtration efficiency is important. This includes the fit of the mask as well as the materials from which it is made. A cloth mask is certainly better than nothing. But now might be a good time to consider upgrading to a surgical mask,” Luby said in a statement. 

The full study can be accessed here.