How Much Does One-Way Masking Protect You From COVID?

As mask mandates are lifted, here's what you need to know before ditching a face covering.
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More and more places are dropping their COVID mask mandates. Recently, several airlines announced that they will no longer require masks to fly after a federal judge voided an extended mandate. Some transit companies, like Uber and Amtrak, followed suit.

The changes are divisive, inspiring both celebration and concern among scientists, public health officials and people simply trying to go about their lives two years into the pandemic. The Centers for Disease Control and Prevention has not changed its stance on public masking, and “continues to recommend that people wear masks in indoor public transportation settings at this time,” the agency states on its site.

All of which raises questions about how to proceed. Should you still mask up when in public, even if you live an an area that no longer requires it? Does it do any good? Here are some important points to keep in mind:

The effectiveness of one-way masking isn’t completely clear...

There isn’t a large, controlled study that directly compares the efficacy of universal masking to one-way masking for preventing the spread of COVID, largely because there are so many variables at play. What’s the setting? What is local transmission like? What types of masks are people wearing, and how well do they fit?

Still, doctors and researchers are pretty much unanimous that universal masking is the gold standard.

“There is no question that it is more effective for both the individual and for public health for a high fraction of people to wear good masks when they are in shared air spaces indoors,” said Alex Huffman, an aerosol scientist at the University of Denver. “Masks act as excellent source control, meaning that they keep the infectious aerosol from going into the room, and they can dramatically reduce the infectious dose that the susceptible person breathes in.”

“Masks act as excellent source control, meaning that they keep the infectious aerosol from going into the room, and they can dramatically reduce the infectious dose that the susceptible person breathes in.”

- Alex Huffman, an aerosol scientist at the University of Denver

The benefits that masks confer multiply when everyone who is in a room — meaning both the infectious person and the person who could become infected — wears a mask, Huffman explained. So the infected person is less likely to spread the virus. The susceptible person is less likely to get infected. And they’re therefore less likely to pass it among themselves and to anyone else they interact with.

A widely covered CDC report from last summer demonstrates the potential limits of one-way masking in indoor group settings. A teacher in Marin County, California, who was occasionally unmasked over the course of two days at work, spread the virus to half of their students — all of whom were masked. Some of those children spread it to family members.

Things have changed since then, so what happens in classrooms may not play out in the same way. For one, that outbreak occurred during the delta surge. But omicron is up to four times more transmissible. On the other hand, it also took place before children ages 5 to 11 were eligible for vaccines. Today they are, though overall vaccination within that age group remains low.

... But one-way masking is certainly better than nothing.

There’s a reason why health care workers have long worn masks in many clinical settings, whether or not their patients were also masked up: The masks protect the person wearing them.

So if you’re in an area of high transmission or you’re simply not comfortable going unmasked indoors, you should take comfort knowing that your mask provides you with an additional layer of protection.

“It is worth doing,” said Dr. Richard Martinello, an associate professor of infectious diseases and pediatrics at Yale School of Medicine. “We have a very simple, safe and effective intervention.”

Martinello pointed to a CDC study that found people who wore a high-grade medical mask in indoor settings had an 83% lower risk of getting COVID than those who did not mask indoors. He noted that it’s impossible to say whether everyone else around them was also masked but said it offers yet more evidence that masking prevents spread of the virus.

Now is the time to pay particular attention to mask type and fit.

If you plan to keep masking up indoors, the type and fit is critical, perhaps now more than ever. Your first choice should be a high-quality medical mask, like an N95, KN95 or KF94. A well-fitted N95 can filter out up to 95% of particles in the air. That recent CDC study on effectiveness of use in indoor settings found that cloth masks and surgical masks are much less effective at preventing COVID spread than these medical-grade masks.

“At this point in the pandemic, especially if you are the only one wearing a mask, I would not bother with anything less than a very high-quality respirator.”

- Alex Huffman

“The quality of the mask filter and the quality of the fit to your face both matter a lot, especially if you’re relying on your mask to do all the heavy lifting to keep you safe from virus in the air you share with others,” Huffman said. “At this point in the pandemic, especially if you are the only one wearing a mask, I would not bother with anything less than a very high-quality respirator.”

Ideally, that would be an N95 or, if you’re in a setting that warrants it, the more substantial elastomeric half mask respirators, he said. But “KF-94-rated masks are very high quality, and KN95 masks can be very good if they are not counterfeit,” he added. (Be careful: The CDC warns that counterfeits abound. Here’s where to buy ones that aren’t.)

Fit matters, too.

“It should seal across the bridge of your nose and be held down by a little metal strip, pull firmly against your cheeks, and seal under your chin and jaw line,” Huffman said. If possible, consider masks with head straps rather than ear loops for a better seal, he recommended.

But remember: masking isn’t the only defense we have in public settings.

Of course, many people — including some health experts — are enthusiastically welcoming the decision to drop mask mandates. They point out that we have layers of protection available to us: We have vaccines and boosters, which lower your risk of becoming infected and, crucially, of becoming severely ill if you do.

Public health experts have also learned a lot about the importance of ventilation in indoor settings. For example, many schools have improved HVAC filters, added portable HEPA filtration and are keeping the windows open, Huffman said. Opening windows in other settings ― like in a ride share, for example ― will also help.

Hand-washing, though not the most exciting of interventions, continues to be important as well.

Those layers mean that masks aren’t the only thing preventing the spread of COVID. They all matter when it comes to stopping transmission.

Experts are still learning about COVID-19. The information in this story is what was known or available as of publication, but guidance can change as scientists discover more about the virus. Please check the Centers for Disease Control and Prevention for the most updated recommendations.

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