Face Masks Protect Wearers, Others From COVID: Studies

By Linda Carroll

December 31, 2020

(Reuters Health) - Two new literature reviews suggest face masks provide some protection to the wearer and when universally worn by the general public they substantially reduce the spread of the new coronavirus.

The reviews, published in Annals of Internal Medicine, look specifically at the effect of masking on COVID-19 transmission.

One report analyzed the impact of masking by the general public on the spread of the virus. Researchers reviewed over 100 research articles and concluded that masking could substantially reduce the spread of viruses, including SARS-CoV-2, without risks to the wearer.

"Our review clearly shows that masks and face coverings worn by members of the public are highly effective in reducing the spread of SARS-CoV-2," said study leader Dr. Thomas Czypionka, head of the Health Economics and Health Policy Unit at the Institute for Advanced Studies in Vienna, Austria and visiting senior research fellow at the London School of Economics and Political Science.

"A growing body of evidence suggests that the virus is transmitted through drops in close contact situations and through aerosols, small particles hovering in the air for extended periods of time that accumulate especially in closed and crowded spaces," Dr. Czypionka said in an email. "Such situations should be avoided of course, but if you can't - for example, on public transport, in shops etc. - masks and face coverings can substantially reduce the risk of infection, mainly by source control, that is, by trapping the particles exhaled. There is also laboratory evidence that they may protect the wearer as well. Therefore, masks can literally save lives, and in a situation like this, with community spread, they should be widely used."

There are many misconceptions about masks, Dr. Czypionka said. "One is that they lead to physiological changes like elevated carbon dioxide levels or decreased oxygen levels in the blood," he added. "Masks and face coverings may cause discomfort for some people, but we found no empirical evidence for masks to cause harm."

The second report -- an update to a "living review" of data on mask use by the general public and by health care workers -- focused mainly on three studies: one study of masking and the prevention of SARS-CoV-2 in a community setting (the DANMASK trial) and two studies of mask use in healthcare settings.

The DANMASK open label trial, which included 6,024 community dwelling adults in Denmark, found that the incidence of SARS-CoV-2 infection among participants was 2%. Surgical mask use as compared to no mask use was associated with a small reduction in risk for infection, but the finding was not statistically significant, the researchers noted.

"The study suggests that masks may have small benefits in reducing the risk of infection in the wearer," said the report's lead author, Dr. Roger Chou, a professor in the School of Medicine at the Oregon Health and Sciences University.

Unfortunately, Denmark is a place where it would be harder to show benefits because the infection rate there is low and people have been good about following guidelines, such as social distancing and handwashing, Dr. Chou said.

"One important reason to wear masks is to prevent those who don't realize they are infected or have mild symptoms from infecting others," Dr. Chou said. "But this study wasn't designed to evaluate that."

Of the two other studies, one, which included 16,397 health care workers and first responders, found that use of an N95 or surgical mask all of the time versus not all of the time was associated with a decreased risk for infection. The second study, which included 20,614 asymptomatic health care workers, found that the risk for infection was reduced with any mask use versus no mask use.

The update of the living rapid review is important, said Juan Jesus Carrero, a professor of epidemiology in the department of medical epidemiology and statistics at the Karolinska Institute in Stockholm. "In interpreting the results of the DANMASK study, it is essential to remember that it was not a study of source control, and therefore doesn't tell us about the ability of community mask wearing to reduce overall transmission in the pandemic," Carrero said in an email.

The new information included in Dr. Chou's study was welcomed by Dr. Catherine Clase, an associate professor in the department of medicine at McMaster University and a member of the Centre of Excellence in Protective Equipment and Materials. "The two additional observational studies on mask wearing are consistent with the expected degree of protection based on the authors' previous work and the meta-analysis on the effects of masks in the transmission of non-COVID coronaviruses," Dr. Clase said in an email.

The Czypionka article highlighted the importance of masking to prevent the spread of COVID-19, Dr. Clase said. "I agree with their assessment that masks can play an important role in reducing the spread of particles of all sizes," she added.

Calling the Czypionka article "outstanding," Carrero applauded the authors for pulling together "a network of evidence on the diverse questions which have surrounded mask use since the beginning of the pandemic. As they summarize, universal community masking has been associated with fewer new cases and lower mortality in every study to examine this question."

SOURCE: https://bit.ly/2L8l6h3 and https://bit.ly/3n3olDD Annals of Internal Medicine, online December 29, 2020.