According to a new modeling study, if enough people wore face masks, even homemade coverings, it would slow the transmission of COVID-19 and prevent further waves of infection.

Cashier scanning products at a grocery store wearing a facemaskShare on Pinterest
New research suggests that widespread use of face masks can prevent a second wave of the pandemic.

All data and statistics are based on publicly available data at the time of publication. Some information may be out of date.

Two mathematical models predict that the widespread use of facemasks in public combined with physical distancing or periods of lockdown provides a way to manage the pandemic and reopen the economy while reducing the risk of future waves of the pandemic.

The authors published their findings in the Proceedings of the Royal Society A.

The models, created by scientists at the University of Cambridge and the University of Greenwich in the United Kingdom, suggest that even homemade masks can dramatically reduce transmission rates, but only if enough asymptomatic people wear them.

People who have recently contracted SARS-CoV-2, the virus that causes COVID-19, take time to develop symptoms — if they develop them at all. During this asymptomatic period, they can unwittingly transmit the virus to others.

When people touch contaminated surfaces and later touch their face, they can contract the virus via their mouth, nose, or eyes.

Transmission through the air happens when people inhale droplets loaded with the virus that a person with the virus expels when they talk, cough, or sneeze. This is most likely to occur in poorly ventilated areas where airborne droplets can accumulate.

In theory, even if face masks are not very good at protecting the wearer, they can prevent a person with the virus from transmitting it to others through the air.

Conclusive evidence has been lacking, however, and some research suggests face coverings are ineffective.

In the United States, the Centers for Disease Control and Prevention (CDC) recommend that people wear cloth face coverings in public, but only in situations where a person is unable to maintain physical distancing.

Similarly, on June 5, 2020, the World Health Organization reversed its earlier skepticism about face masks to advise that people wear them in public places where it is impossible to maintain adequate physical distancing.

In the United Kingdom., face coverings will be compulsory on public transport from June 15, 2020.

However, the new modeling study suggests that people should not restrict the wearing of masks to public transport and other places where they might find it difficult to maintain physical distancing.

“In the U.K., the approach to face masks should go further than just public transport,” says Professor John Colvin of the University of Greenwich, one of the authors. “The most effective way to restart daily life is to encourage everyone to wear some kind of mask whenever they are in public.”

For their study, the scientists modeled scenarios involving different initial infection rates, face mask effectiveness, the extent of adoption with social distancing, and periods of lockdown.

They did this by combining population-level models with evidence about how the virus spreads between individuals via the air and contaminated surfaces.

Their models predicted that it would be possible to bring an outbreak under control if people had to wear a mask in all public places. They say this would apply even if the masks were not very effective at preventing transmission to other people.

An outbreak starts to wane when the average number of other people that a person with the virus infects – known as the “R’ number, or R0 – falls below 1.

The models predicted that if the masks were 75% effective, wearing them could bring the ‘R’ number to below 1 from a high starting point of 4.

If the masks were only 50% effective, the “R’ number could fall to below 1 from a lower starting point of 2.2.

The scientists of this study believe that their figures may be pessimistic as previous research suggests that even a homemade face mask made from a cotton T-shirt is at least 90% effective at preventing transmission to other people.

The scientists report that under all their scenarios, routine face mask use by at least 50% of the population brought the outbreak under control, reducing R0 to less than 1.

Some experts have concerns that wearing a mask might increase a person’s risk of contamination if they repeatedly touch their face, for example, to adjust the mask.

But the study found that masks were still beneficial at a population level, even under the assumption that a person quadruples their risk of infection due to repeatedly touching their face.

Lead author Dr. Richard Stutt, who is part of a team that usually models the spread of crop diseases at the University of Cambridge’s Department of Plant Sciences, said: “Our analyses support the immediate and universal adoption of face masks by the public.

“If widespread facemask use by the public is combined with physical distancing and some lockdown, it may offer an acceptable way of managing the pandemic and reopening economic activity long before there is a working vaccine.”

To persuade enough people to wear masks in public, he believes the message from governments should be: “my mask protects you, your mask protects me.”

In common with all modeling studies, the team had to make certain assumptions, sometimes based on limited evidence.

Prof. Keith Neal, Emeritus Professor of the Epidemiology of Infectious Diseases at the U.K’s University of Nottingham, who was not involved in the research, said:

“Clearly there is some face validity to the suggestions that the more people who wear masks, the more impact this might have on the spread of COVID-19, but this is highly dependent on the effectiveness of the masks the public will use […] Also, the model itself has six parameters (particularly about infectiousness of droplets and spread of different types of infectious material) which were arbitrarily defined.”

“The findings of the model, like all other models, is highly dependent on the assumptions made on these parameters. If any of the assumptions are significantly wrong, this will affect the conclusion of the study.”

– Prof. Keith Neal

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