ARI SHAPIRO, HOST:
About 70% of people in the U.S. live in places where COVID cases and hospitalizations are now low enough that masks are no longer necessary, according to new guidelines from the Centers for Disease Control and Prevention. Of course, not everyone is ready to shed their masks, which made some of us wonder, does it make sense to mask up when others around you don't? NPR health reporter Will Stone has been looking into this. Hey, Will.
WILL STONE, BYLINE: Hello.
SHAPIRO: All right, the CDC says it's OK to take off your mask in most places. Some infectious disease experts say they aren't so sure. What's the counterargument here?
STONE: Yeah. Well, some are telling me they are not ready at all to take off their masks in any public setting just yet. Others are trying to find, I would say, more of a middle ground. And this is how Dr. David Dowdy is thinking about masking in his life. He's at the Johns Hopkins Bloomberg School of Public Health.
DAVID DOWDY: My level of comfort going into a very crowded venue - I'm going to need to see the case counts go a lot lower than they are, whereas going to a less crowded spot or well-ventilated area, I would be comfortable.
STONE: So people need to make their own personal decisions based on the infection rate where they live, whether they have underlying health risks or live with someone who does. All of that comes into play.
SHAPIRO: All right. So let's imagine that Dr. Dowdy walks into a crowded concert venue. Nobody's wearing masks except for him. How protected is he in that scenario?
STONE: Well, he could be pretty well-protected if he is doing things right. So what does that mean? A big part of this is what you're putting on your face, and the consensus is you just cannot count on a cloth or surgical mask if no one around you is wearing anything. What you need is really an N95 or something comparable, like a KN95. And that's because they block the large respiratory droplets and the tiny airborne particles that can carry the virus. Many people already do wear these. Those who treat COVID patients, like Dr. Abraar Karan at Stanford, have relied on N95s throughout the pandemic.
ABRAAR KARAN: I've taken care of hundreds of patients with COVID-19 over the last two years, and I've been very close to them. A lot of the patients were coughing and had symptoms and weren't able to wear masks. And I never got COVID from a patient.
STONE: Now, it is worth pointing out that health care workers like Karan get fit tested to make sure their mask is sealed well. That's obviously not something most of us are able to do.
SHAPIRO: Does having a less-than-perfect fit make it not worth wearing the mask at all?
STONE: Not at all. It is still very valuable. This is not all or nothing. And one person who knows a lot about this is Lisa Brosseau. She's an industrial hygienist with the Center for Infectious Disease Research and Policy at the University of Minnesota. And she says an N95 that's not fit tested is still better than a surgical or cloth mask.
LISA BROSSEAU: You can get something that you're pretty sure fits well on your face. You know, you form the nose clip. You put both straps over your head. You don't have big gaps under your chin or around your nose. You can be assured that you're probably going to get pretty good protection.
STONE: Brosseau has actually studied how well the average person does with fitting their N95, and she found most can get a fit that will let about 20% of particles get through. And she compares that to health care workers, who get about 10% leakage over the course of a day.
SHAPIRO: What does all that mean in practice, especially if you're the only one wearing a mask?
STONE: Yeah. It really depends on things like how crowded it is, how long you spend indoors, the ventilation. One modeling study from Germany found you'd have about a 20% risk of getting infected after an hour. And this is assuming you have on an N95 and you're near someone who's unmasked and contagious. Lisa Brosseau did her own calculations, and she concluded you'd have about an hour and 15 minutes until potentially getting infected. But I do want to be really clear. You know, there are some big assumptions here. You know, these are estimates that can give you a rough sense. The bottom line is a mask can help you. It can't totally eliminate risk.
SHAPIRO: That's NPR's Will Stone. Thanks, Will.
STONE: Thank you.
(SOUNDBITE OF DJANGO REINHARDT'S "FINE AND DANDY") Transcript provided by NPR, Copyright NPR.