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Delta is raging. Is it really safe to send kids back to the classroom?

We talk to Harvard professor Joseph Allen, one of the world’s leading experts on healthy air, about whether delta should make parents worried.

Delta is raging. Is it really safe to send kids back to the classroom?
[Images: channarongsds/iStock, Dan Forer/Getty Images]
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“My son is going back to school in September, no matter what!” I concluded in June, with COVID-19 vaccines working miracles, and infection rates dropping. Then, the delta variant hit, proving to be more contagious than the COVID-19 we knew during the last school year.

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Over the past few weeks, I, perhaps like many other parents out there, have been second-guessing myself, wondering if it’s actually safe to send my grade schooler back. So I reached out to Joseph Allen, one of the world’s leading authorities on indoor air quality. He’s an associate professor at Harvard’s School of Public Health. He’s also on the COVID-19 Commission of the respected medical journal, The Lancet, and author of the book Healthy Buildings. His key takeaway? While parents are right to worry, simple mitigation efforts can make classrooms safe.

Yes, delta is alarming in both how quickly it spreads and the fact that it can spread among vaccinated people—which makes it worrisome for teachers, staff, and older vaccinated students. However, it does not appear to make children sicker than previous COVID variants. “The evidence out of other countries does not suggest that delta harms kids disproportionately or more than the prior variant,” Allen says. “The difference with delta is that it spreads more quickly, and that means more kids can get infected.”

[Photo: Tatiana Malkova/iStock]
Even though it’s easier for a child to become infected with delta, Allen insists that much of the 18 months of general understanding that we have about COVID-19 still holds true. The absolute risk of a child being hospitalized due to COVID-19, even during delta, is “on the order of 3 to 4 kids per million,” says Allen. A recent study published in Nature found that the absolute risk of kids 18 and under dying of COVID-19 was 2 in a million. It’s a tragedy we should do everything we can to avoid. But comparatively, 1 in 103 of us will die in a car crash.

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“The single most important thing is that kids are in school,” says Allen, pointing out that education and socialization are key to childhood development, and that we’re beginning to see the costs of closing schools in 2020, such as increased rates of childhood depression and even suicide. “. . . [I]t’s not like we don’t know how to keep kids and adults safe in school.” Here are Allen’s key recommendations for setting up the safest school environment possible.

Get everyone vaccinated who can be

Allen says without hesitation that children and staff should wear masks in schools. (We already know this, even though several states have attempted to bar mask mandates.)

But even more than that, Allen points to vaccination as a “silver bullet” against delta transmission. Everyone who sets foot in a school who can be vaccinated should be vaccinated for COVID-19, just as they are for measles in all 50 states.

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While individual stories of delta breakout cases are scary, Allen urges us to look at the larger trend afoot: We can see in states with high vaccination rates, the delta surge is less pronounced overall. There’s also plenty of evidence that, over the past 18 months, COVID-19 has spread very little in schools that took proper safeguards, and the CDC expects students will only be safer as more staff is vaccinated—assuming people get vaccinated.

“It is absolutely appalling to see the low vaccination rates for school workers,” says Allen. “Vaccines should be mandatory for everyone in school—teachers, staff, and everyone over 12. People are acting like this is some affront to our liberties; it’s not, it’s routine. We get vaccinated all the time for all sorts of things, and we have to show a vaccination record.”

Focus on air quality

COVID-19 is airborne, and delta appears to be more transmissible through the air than earlier variants. Our best infrastructural defense strategy to an airborne virus floating inside is what building experts call “air changes per hour,” which is abbreviated to ACPH or ACH.

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It’s not complicated. That measurement points to how many times the air in a room is refreshed in any given hour. But what’s the right ACPH?

“We [at the Harvard Healthy Buildings Team] recommend school classrooms get four to six air changes per hour, through any combination of ventilation or filtration,” Allen says.

Why four to six? Why not more? Why not less? “It’s not like we picked it out of thin air,” says Allen. “It’s what hospitals use, and have used, for years.” And even while COVID-19 patients have filled hospitals, most frontline healthcare workers haven’t contracted COVID-19 at a greater rate than anyone else. PPE, like masks, are likely a big reason for that, but refreshing hospital air is, too.

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[Photo: KangeStudio/iStock]
ACPH can come in the form of three main sources. A teacher can open windows and the classroom door to circulate air from outside. A school’s central HVAC system can be upgraded with MERV 13 air filters to help scrub the air clean. Or a teacher can set up portable HEPA filter air purifiers (as long as they make sure the purifier is right for the room size). Combinations of ventilation and filtration can be used, just as long as they reach this circulation target, Allen says.

Why haven’t you heard of the four to six ACPH rule of thumb? It might be because neither the CDC nor the World Health Organization (WHO) has set up an air circulation target for classrooms. However, your school can reference this handy 5-step guide out of Harvard to assess air circulation in your child’s classroom.

But what if your school doesn’t have the funding to upgrade its central HVAC system or buy portable air filters? Allen points to a $112 billion chunk in the American Rescue Plan (passed in March 2021) that’s been earmarked specifically for schools to invest in upgrades to combat coronavirus in classrooms. Those upgrades can include mechanical HVAC upgrades, portable air filters, and even air sensors for teachers to use to test air quality rates. “If you’re part of a school or district and haven’t worked to improve your filtration system, you’re failing those kids,” says Allen.

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Should schools go with central air upgrades or air purifiers?

There’s still time for schools to claim these government funds and upgrade air filtration during the 2021 school year. Allen suggests that schools “definitely” prioritize upgrading their central HVAC systems first to ensure they are reaching air circulation targets, and support MERV 13 filtration, instead of installing portable air filters, whenever possible.

Centralized high-grade air filters often require newer, more robust air circulation systems than some old schools have, simply because it’s harder to suck air through a good filter than a lousy one.

The reason that Allen prefers that schools upgrade their central HVAC over buying air purifiers isn’t because air purifiers don’t work. He simply sees the investment in central building air as having a better payoff in the long term.

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New HVAC systems, he explains, run more efficiently, which lowers a school’s energy bills. Also, these systems create better ecosystems for children to learn in. “In schools with higher ventilation rates, we see higher performance on test scores and fewer missed school days,” says Allen. “It comes with a whole host of positive benefits.” For more, the U.S. Department of Education lists specific ventilation upgrades that every school should think about.

Allen reiterates that schools need to be taking advantage of public funding to improve their air quality. And if your school district hasn’t reached out about such upgrades, you should bug them. “Yes, write them,” says Allen. “If they’re not doing [sharing a ventilation upgrade plan], or haven’t communicated it to parents . . . every parent should be writing their school asking what they did over the past 18 months to the school building to improve ventilation or filtration. If they didn’t act, it’s just a total and gross failure of leadership in the school district. There’s no other way to say it, to soften it.”

About the author

Mark Wilson is a senior writer at Fast Company who has written about design, technology, and culture for almost 15 years. His work has appeared at Gizmodo, Kotaku, PopMech, PopSci, Esquire, American Photo and Lucky Peach

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