Masks work to prevent COVID-19

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A large real test of face masks in Bangladesh shows that the masks work to reduce the community spread of COVID-19. It also shows that surgical masks are more effective than fabric face covers.

The study, which was published ahead of the peer review, demonstrates the power of careful investigation and offers a wealth of mask-wearing lessons that will be important around the world. One of the main findings of the study, for example, is that wearing a mask does not encourage people to abandon social distancing, something public health officials feared would happen if masks gave people a false sense of security.

“What we have really been able to achieve is to demonstrate that the masks are effective against COVID-19, even as part of a rigorous and systematic assessment that was carried out during the throes of the pandemic,” said Ashley Styczynski, MD, who was an infectious disease researcher. at Stanford University when she collaborated on the study with other colleagues at Stanford, Yale, and Innovations for Poverty Action (IPA), a large nonprofit research and policy organization currently working in 22 country.

“And so, I think the people who insisted on wearing masks because [they] I felt like there wasn’t enough evidence for that, we hope it really helps bridge that gap for them, ”she said.

It included over 600 unions – or local government districts in Bangladesh – and around 340,000 people.

Half of the districts received cloth or surgical masks as well as continuous reminders to wear them correctly; the other half was followed without any intervention. Blood tests of people who developed symptoms during the study confirmed their infections.

Compared to villages that did not wear a mask, those in which masks of any type were worn had about 9% fewer symptomatic cases of COVID-19. The result was statistically significant and it is unlikely that it was accidental.

“Someone could read this study and say, ‘OK, you’ve reduced COVID-19 by 9%. Big problem. “And what I would respond to is if anything, we think it’s a substantial understatement,” Styczynski said.

One of the reasons they think they underestimated the effectiveness of the masks is that they only tested people who had symptoms, so people who had only very mild or asymptomatic infections were missed.

Another reason is that among people who showed symptoms, only a third agreed to have a blood test. The effect could have been greater if participation had been universal.

Local transmission may also have played a role. Bangladesh’s COVID-19 rates were relatively low during the study. Most infections were caused by variant B.1.1.7, or Alpha.

Delta has since taken over. Delta is believed to be more transmissible, and some studies have suggested that people infected with Delta shed more virus particles. Masks can be more effective when more viruses are circulating.

Investigators also found significant differences by age and type of mask. Villages in which surgical masks were worn had 11% fewer COVID-19 cases than villages in which masks were not worn. In villages where cloth masks were worn, on the other hand, infections were only reduced by 5%.

The cloth masks were substantial. Each had three layers – two layers of fabric with an outer layer of polypropylene. In testing, the filtration efficiency of the cloth masks was only around 37%, compared to 95% for the three-layer surgical masks, which were also made of polypropylene.

Masks were more effective for the elderly. People aged 50 to 60 who wore surgical masks were 23% less likely to test positive for COVID compared to their peers who did not wear masks. For people over 60, the risk reduction was greater – 35%.

Rigorous research

The study took place over an 8 week period in each district. The interventions took place in waves, the first starting in November 2020 and the last in January 2021.

Investigators gave each household a free rag or surgical masks and showed families a video on wearing an appropriate mask with promotional messages from the prime minister, a chief imam and a national star of the cricket. They also distributed free masks.

Previous studies have shown that people don’t always tell the truth about wearing masks in public. In Kenya, for example, 88% of people who responded to a telephone survey said they regularly wear masks, but researchers found that only 10% actually did.

Investigators in the Bangladesh study not only asked people if they had worn masks, they stationed themselves in public markets, mosques, tea stalls and on the roads that were the main entrances. villages and took notes.

They also tested various ways to educate people and remind them to wear masks. They found that four factors were effective in promoting the wearing of masks, and they gave them an acronym – NORM.

• N, for free masks;

• O, for offering information through video and local leaders;

• R, for regular reminders to people by investigators who stand in public markets and offer masks or encourage anyone who is not or was wearing them properly;

• M, for modeling, in which local leaders, such as imams, wear masks and remind their followers to wear them.

These four measures tripled the wearing of masks in intervention communities, from a baseline of 13% to 42%. People continued to wear their masks correctly for about 2 weeks after the study ended, indicating that they had become accustomed to wearing them.

Styczynski said nothing else – not SMS reminders, signs posted in public places, or local inducements – moved the needle on wearing the mask.

Lives and money saved

The study found that the strategy was also profitable. Giving masks to a large population and getting people to use them costs around $ 10,000 per life saved from COVID, on par with the cost of rolling out mosquito nets to save people from malaria, Styczynski said.

“I think what we have been able to show is that this is a really important tool to use around the world, especially since countries have delays in accessing and deploying vaccines.” , she said.

Styczynski said masks will continue to be important even in countries like the United States, where vaccines do not stop transmission 100% and where a large portion of the population is unvaccinated, such as children. .

“If we want to reduce COVID-19 here, it’s really important that we consider the continued usefulness of masks, in addition to vaccines, and that we don’t really see them as one or the other,” a- she declared.

The study was funded by a grant from GiveWell.org. The funder played no role in the design, interpretation or decision to publish the study.

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