It seems intuitive that the best approach to reopening is to compromise: If we meet the virus halfway, then surely we can have more normal lives and avoid widespread community transmission. This intuition is part of the fuel behind the enthusiasm for “hybrid” plans for school reopening, in which groups of children alternate periods of in-person instruction with remote learning. But unless they are prepared very carefully indeed, hybrid plans can be among the most risky of all — especially if the main goal is to prevent the virus getting into schools. The reason is the networks the virus uses to transmit itself.

Imagine a hybrid plan like the one being considered by Boston Public Schools for all grades. Here, students are split into two groups that have in-person instruction either Monday and Tuesday or Thursday and Friday, with the schools getting thoroughly sanitized on Wednesdays (a third group, including those learning English or with special educational needs, study in person all four days). When they do not have in-person instruction, students will be learning remotely. Alternatives to this would be to have different groups of kids alternating in-person instruction weekly or even daily.

These all sound superficially reasonable. So what’s the problem?

The problem is what happens on the days when students are supposed to be remote learning. Most parents will struggle with work commitments, and that will be especially true for the large number of parents who cannot work from home. They will need child care. That could mean a family member (maybe one in an older at-risk age group), a part-time nanny or a gathering of groups of families for kids to learn remotely together, with parents taking turns supervising. What all of these have in common is that they introduce additional contacts beside the ones that happen in school or in the families on their own — which the school cannot monitor for adequate protection or test (and yes, schools should be testing).

Hybrid school plans make it easier for the virus to transmit into schools, simply by producing more links between schools and families along which the virus can travel.

Under closer inspection, there are other practical problems with hybrid plans, too. While they superficially give parents the appearance of some normalcy, they can place huge burdens on teachers, who need to master remote learning and in-person instruction. What about those teachers who are parents themselves, but live in a different school district which has adopted a different hybrid plan?

We can divide risks in schools into three categories: risk to children, risk to those they might infect and risk to the community as a whole. It is true that the risk to children from infection with the novel coronavirus is very low indeed. It is not nil, but small risks are unavoidable, or none of us would ever get in a car. There is almost certainly a higher risk overall to kids from the negative effects of schools remaining closed than there is from the virus directly.

The risks to caregivers, teachers and other staff, however, are higher. These groups are much more likely to suffer severe consequences than kids are, being older. As a result we want to minimize the chances they are exposed, which means reducing the numbers of routes by which the virus can find its way into the school, which means limiting the contacts between host networks. It is straightforward — we want to minimize school outbreaks as much as possible to protect others, and the less we introduce the virus to schools, the fewer opportunities for outbreaks there will be. In countries like Sweden, where some schools stayed open throughout the spring wave, teachers were as likely to become infected as “other professions,” but this does not mean school outbreaks do not happen. In fact, it suggests they do, but they are not detected due to lack of testing. That only means children are not a disproportionately large source of infections. Which brings us to the risk to the community.

Responsible leaders have been clear that open schools depend on low levels of community transmission. If we open schools, they will provide some opportunities for the virus to transmit, and so as I and others have argued, we need to remove opportunities for transmission elsewhere, be it bars, restaurants, casinos, fitness centers or other places. If communities are smart, they will do this before opening schools, so they start school with less community transmission in the first place. Which businesses must be closed will be a tough choice, and some people will not like leaders for it whatever they decide — but nowhere near as much as the parents will not like them if schools close.

Instead of cycling students through schools and ad hoc child-care solutions, we could prioritize in-person instruction for those for whom remote learning will not work, whether because the kids are too young, their parents are essential workers or for other reasons. These decisions should be made on the basis of need. As with other features of the pandemic, there are no perfect solutions. But some are better, fairer and more sustainable than others.

Saying that opening schools should be “a priority” does not mean it is actually being prioritized. The problem is ghastly, and I am sincerely grateful to everyone in education who has worked so incredibly hard to help in-person instruction be as unlikely to produce an outbreak as possible. But on top of all the personal protective equipment, distancing and hand sanitizer, we should remember that prevention is best. The less the virus gets into the schools, the less damage it can do in them. Hybrid reopening plans risk opening the door for it.

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