18-01-2021

One Mask Is Good. Would Two Be Better?

Football coaches do it. Presidents-elect do it. Even science-savvy senators do it. As cases of the coronavirus continue to surge on a global scale, some of the nation’s most prominent people have begun to double up on masks — a move that researchers say is increasingly being backed up by data.

Double-masking isn’t necessary for everyone. But for people with thin or flimsy face coverings, “if you combine multiple layers, you start achieving pretty high efficiencies” of blocking viruses from exiting and entering the airway, said Linsey Marr, an expert in virus transmission at Virginia Tech and an author on a recent commentary laying out the science behind mask-wearing.

A double-mask wearer in New York City in April. Credit...Kena Betancur/Getty ImagesCaption

Of course, there’s a trade-off: At some point, “we run the risk of making it too hard to breathe,” she said. But there is plenty of breathing room before mask-wearing approaches that extreme.

A year into the Covid-19 pandemic, the world looks very different. More than 90 million confirmed coronavirus infections have been documented worldwide, leaving millions dead and countless others with lingering symptoms, amid ongoing economic hardships and shuttered schools and businesses. New variants of the virus have emerged, carrying genetic changes that appear to enhance their ability to spread from person to person.

And while several vaccines have now cleared regulatory hurdles, the rollout of injections has been sputtering and slow — and there is not yet definitive evidence to show that shots will have a substantial impact on how fast, and from whom, the virus will spread

Through all that change, researchers have held the line on masks. “Americans will not need to be wearing masks forever,” said Dr. Monica Gandhi, an infectious disease physician at the University of California, San Francisco, and an author on the new commentary. But for now, they will need to stay on, delivering protection both to mask-wearers and to the people around them.

The arguments for masking span several fields of science, including epidemiology and physics. A bevy of observational studies have suggested that widespread mask-wearing can curb infections and deaths on an impressive scale, in settings as small as hair salons and at the level of entire countries.

Doctors intubate a Covid-19 patient in a California hospital, as cases surpassed 90 million and deaths near 2 million. Photo: ReutersCaption

One study, which tracked state policies mandating face coverings in public, found that known Covid cases waxed and waned in near-lockstep with mask-wearing rules. Another, which followed coronavirus infections among health care workers in Boston, noted a drastic drop in the number of positive test results after masks became a universal fixture among staff. And a study in Beijing found that face masks were 79 percent effective at blocking transmission from infected people to their close contacts.

The point is not to make a mask airtight, Dr. Marr said. Instead, the fibers that comprise masks create a haphazard obstacle course through which air — and any infectious cargo — must navigate.

“The air has to follow this tortuous path,” Dr. Marr said. “The big things it’s carrying are not going to be able to follow those twists and turns.”

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