ARI SHAPIRO, HOST:

Many kids going back to school are still too young to be vaccinated, and so parents are asking what schools should be doing to minimize the risks to their children. NPR health correspondent Maria Godoy has some answers.

Hi, Maria.

MARIA GODOY, BYLINE: Hi, Ari.

SHAPIRO: We know the delta variant is very contagious. What does that mean in the context of a classroom where kids may not be vaccinated?

GODOY: Well, it can spread much more easily, and we have some real-world evidence of that. One good example is a study put out recently by the CDC that looked at an outbreak that occurred in late May in an elementary school in California. On the surface, it looked like the school was doing a lot of things right. They were masking. They were spacing out desks. And yet a teacher there passed the virus on to half the class. Now, this teacher wasn't vaccinated and had gone to work with really mild allergy-like symptoms. At brief points during the day, the teacher took their mask off to read out loud to the class.

SHAPIRO: And is that how the disease was spread to the children?

GODOY: Well, you know, the teacher got a coronavirus test and it came back positive. And yeah, then soon after, half the class ended up testing positive, too. And it wasn't just kids in that one classroom. The outbreak spread to other classrooms, siblings of students and even fully vaccinated parents. In fact, all told, there were 27 people infected.

SHAPIRO: So it seemed to be two key factors here - the teacher took the mask off and also was not vaccinated.

GODOY: Right. Right. And both of those factors are critical. In fact, experts say that with delta, there's little margin for error when it comes to these kinds of protections. I talked to Tracy Lam-Hine. He's the Marin County epidemiologist who led the study. He says all the kids were masked in that classroom, and the teacher was, too, for the most part.

TRACY LAM-HINE: For me, the takeaway of this story really is that even just momentary short, brief lapses in, you know, taking off a mask can open up an opportunity for delta to escape through.

GODOY: And remember - for kids under 12, they're too young to be vaccinated, which makes masking one of the most important protections they have.

SHAPIRO: But also there was the vaccination element here. How different might this have gone if the teacher had been vaccinated?

GODOY: You know, that's a good question. Public health officials say it's critical that anyone who spends time indoors with kids should get vaccinated. And that includes kids 12 and older who are now eligible for the vaccine. This creates a kind of protective cocoon around those unvaccinated kids. Jason Newland is a pediatric infectious disease doctor at Washington University in St. Louis. He says there's data that the more adults are vaccinated, the lower the rate of infections is among kids.

JASON NEWLAND: Israel has some really interesting data, right? When they saw that their vaccine rates of their adults got really, really high, they actually drove down their rates in kids, which I think goes to show - right? - the cocooning thing works.

SHAPIRO: So masking and vaccination are two important points. What else can schools be doing to protect kids?

GODOY: Good ventilation - experts say that's paramount because we know this fire spreads primarily through the air. Viral particles can accumulate indoors and linger, sometimes for hours. Jose-Luis Jimenez at the University of Colorado Boulder studies aerosols. He says think of virus particles like cigarette smoke in a room. It might start off hovering just around the person who's smoking.

JOSE-LUIS JIMENEZ: But after half an hour, after 10 minutes, the whole room is filled with smoke.

GODOY: And what do you do when a room is filled with smoke? You open windows and doors. And so the same thing applies here. You also want to use high-quality air purifiers, the ones that use a HEPA filter. And finally, move activities outdoors as much as possible, especially lunch when kids are unmasked. The bottom line is, these strategies aren't perfect on their own, but the more protections you can layer on in schools, the better the chance that you can curb the spread of the virus.

SHAPIRO: That's NPR health correspondent Maria Godoy.

Thanks, Maria.

GODOY: My pleasure.

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