COVID-19 Data Dives: The Many Ways Opening Schools Could Go Wrong

William P. Hanage, PhD


August 11, 2020

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William P. Hanage, PhD

The dilemma of what to do about schools during a pandemic has opened a floodgate of opinions written by a whole host of experts and not-so-experts recently. I hope to add something useful to that mix.

Point 1. All kids are not alike. Older kids transmit like adults. It's hard to say that high schools "drove" the surge in Israel following wide reopening, but it's clear that they didn't help matters.

Point 2. Studies of household transmission in kids are biased. Look for symptoms to detect index cases and you're not going to catch the kids, who are less likely to have symptoms. Did I mention that nonsymptomatic transmission is a thing

Point 3. Schools are hard to study because we closed them early in the pandemic and at a point when we didn't really have good testing. Understanding what did happen is hard enough; what would have happened is even harder to guess. 

It's important to understand that statements like "there was an introduction to the school without transmission!" are not so helpful. The unusually high degree of variability in transmissibility means that we expect that a lot of people won't transmit, but those who do can transmit to a lot of secondary cases. These are superspreading events. We need better population data, not anecdotes. 

What I Think

Consistent data from household studies suggest that younger kids are less likely to get infected, and if they do, they are less likely to transmit. But that's not enough to say that younger kids going back to school isn't a risk. The contacts that kids make in schools are different from household contacts.

This is where a study comparing Finland and Sweden, two neighboring countries with very different approaches to the pandemic, comes in. Both shut down high schools and colleges, but Sweden kept schools for younger kids open.

The data about the younger kids in this study aren't so reliable because, as the report itself says, they are probably massively underestimating infection in children as, like everywhere else, testing was diverted to severe cases that occurred elsewhere in older cohorts. So ignore that. However, the limited testing in children can't explain the fact that people working with those younger kids were no more likely to be infected than people working in other professions. 

I should point out that in Sweden, this risk has been pretty high. Sweden has had a rather high force of infection (rate at which susceptible individuals acquire a disease) in the community and a resulting high per capita mortality rate. But this suggests that the toll of the virus was not specifically driven by schools for younger kids. This should be comforting-ish.

On the other hand, think back to what I said about variability in transmission. This is what leads to so-called "superspreading events." What would a superspreading event from an infected child in an elementary school classroom look like?

Let's assume that a lot of classmates, and the teacher, all get infected. If you are only testing those who become ill, that means you are much more likely to detect the case in the teacher who, as an adult, is more likely to be symptomatic, but not the cases in the schoolchildren. In fact, many places are still refusing to test asymptomatic contacts, which systematically ruins our ability to detect transmission in children.

Given the variation in transmissibility, most of those kids won't transmit. But it only takes one of them to infect an older family member who works in one of those "other professions" the Swedish study compares with teachers to equal an infection in the school teacher. You see where I am going with this. It would be better to ask whether being a parent of kids in school was a risk factor for being infected.

Older kids, on the other hand, seem to transmit like adults — adults that have trouble social distancing. What a surprise. This is really important for colleges. I cannot support in-person instruction in the fall. 

A personal thought: Younger kids struggle with remote learning because, you know, they can't read yet. Maybe prioritize them for in-person learning. Focus the online stuff on kids who get the technology and might even enjoy it. 

As for older kids, I know it will be really hard, but this is the age group most likely to contribute to illness in the community and to be ill themselves. It's not easy, but limitations will be necessary, even among age groups less likely to party in dorms. 

Personally, I'd recommend online only as much as possible for age groups that can read, after a few weeks to bond with teachers, ideally outside. I am, however, happy to have this view improved by actual educators. All I know is infectious disease. 

Boston public schools are one of many systems considering a "hybrid" teaching model in which kids alternate, with half the class in school half the week and the other half the other.

I think this is flawed. Here's why: When these kids are not in school, what happens to them? Their desperate parents will reasonably seek childcare. And in doing so, they introduce new contacts through those caregivers. New contacts equals more opportunities for transmission into the schools. Which is, err, bad? 

And you know what? Because those additional contacts are outside the school system, you can't bring them into whatever brilliant testing regimen the school district puts in place. 

The biggest remaining question is, what happens when things get bad again? We expect that they will at the very least get worse. There is so little grown-up, informed, thoughtful input being put into practice — though I know there are a lot of grown-up, informed, thoughtful people offering input.

Bill Hanage is an associate professor at the Center for Communicable Disease Dynamics in the Department of Epidemiology at the Harvard T. H. Chan School of Public Health. He specializes in pathogen evolution. Follow him on Twitter.

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