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Opinion Covid-19 cases will likely rise again in the fall. Here’s how to keep schools open.

Students play at an elementary school in San Francisco on Oct. 5. (David Paul Morris/Bloomberg)
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Joseph G. Allen is an associate professor and director of the Healthy Buildings program at Harvard University’s T.H. Chan School of Public Health. Michael Mina is an assistant professor of epidemiology at the Chan School and assistant professor of pathology at Harvard Medical School.

Let’s make one thing clear: Covid-19 cases in the United States will likely rise in the fall and early winter. Coronaviruses are seasonal; this virus is no different.

As a result, the United States may be tempted to close schools in response, as recently happened in Britain and Singapore. That would be a mistake. Here’s what we can do to ensure it doesn’t happen.

Should the United States experience a surge in the fall, it will be nothing like the deadly surge from last winter, which claimed more than 3,500 lives per day. The vast majority of deaths — 80 percent — occurred in those older than 65. That age group is now 85 percent vaccinated with at least one dose. So even with ongoing spread, death rates will drop.

What we can expect this winter is an increase in cases from unvaccinated adults and kids. One of those is more concerning than the other.

The risk of death for someone older than 65 who is unvaccinated is 1 in 1,000, but the risk of death for someone younger than 19 is 1 in 1,000,000. Dylan Morris of UCLA brilliantly explained why in a recent essay. Fighting off a new virus can be a big problem for adults. But for kids, every virus they see is novel, and, fortunately, their bodies have evolved to tolerate the novelty.

Case counts may be low overall, but pockets of outbreaks will still rise. In places such as New England, where adult vaccination rates are approaching 80 percent, this may not be an issue. But in places such as Mississippi, where they are 43 percent, this will certainly be a bigger problem.

The No. 1 thing we can do is continue vaccinating like crazy and reaching communities where immunization rates are lowest — especially Black and Hispanic communities, and Republican men.

But we should also be preparing schools for any potential “surges.” Even though such surges are poor indicators for the risk kids face, and teachers will have had access to vaccines for months, it’s worth neutralizing the threat so that schools can resist pressure to close.

First, we must heavily invest in rapid tests. If a kid has cold symptoms this fall, we want to be sure we’re not isolating them inappropriately or quarantining an entire classroom for two weeks. Rapid, on-site tests can clear that right up.

Quarantining is a strategy that is used when we don’t know if a potentially exposed person is infected and a risk to others. But with rapid tests, which take just 60 seconds in the morning, we don’t have to guess who is infectious. If negative, a rapid test can offer high confidence that a person is not infectious and can go to school.

Rapid tests can also dramatically cut down on isolation time for those who are infected. As we have been arguing tirelessly for more than a year, PCR tests can detect the virus at such low levels that they are meaningless in terms of infectiousness because they can stay positive for weeks after someone is infectious. If a student or worker is out because of a positive test, they should be instructed to do a rapid test every day. Once they have two days of negative tests, which means they’re no longer infectious, they should be cleared to come back to work or school.

Second, schools should use stimulus funds to improve their ventilation and filtration to help reduce airborne transmission of the virus. The first thing to do is understand what their buildings can and can’t do. Hire a good mechanical engineer or commissioning agent to assess and optimize existing systems, like a tuneup for a car.

Once schools know what they have, they should prioritize increasing the amount of fresh outdoor air and upgrading filters to MERV 13 or higher to achieve four to six air changes per hour of “clean” air in every classroom. If that’s not possible and if opening windows doesn’t produce enough ventilation (in many cases it does), schools can always use portable air cleaners with HEPA filters. These are a cheap and effective way to get clean air in schools. A rule of thumb is to buy a device with a clean air delivery rate of 350 for every 500 square feet.

As for masks, we were early proponents of mask-wearing, and now one of the earliest to say masks are not needed for kids in schools in the fall. But also, it’s one of the easiest interventions to reinstitute in the event something unexpected happens this fall. Kids can put away their masks with their winter coats and take them out again when the weather turns, if needed.

After most disasters, such as a hurricane, people pick up the pieces and plod along in their recovery in a linear fashion. That’s not how pandemics work. We have to be flexible in our response, scaling up controls as cases rise and pulling back on some controls when things look better. No matter what, however, closing schools should be off limits.

Read more:

Leana S. Wen: The pandemic isn’t over — especially for our children

The Post’s View: Summer school is more important that ever. A teacher shortage may deny students the opportunity.

The Post’s View: Schools must use relief money to provide what students need, not what adults want

Tracy Beth Høeg, Lucy McBride, Allison Krug and Monica Gandhi: It’s time for children to finally get back to normal life

Micheline Maynard: Those $300 pandemic checks aren’t the only reason restaurant employees might not want to go back to work