Nobody should claim that children cannot transmit this virus, or that schools are “safe” during the pandemic the same way that, say, talking on the telephone with a sibling who lives 2,000 miles away is safe.

But people under 18, and young children especially, are less susceptible to infection, less likely to experience severe symptoms, less likely to be hospitalized or die, and less likely to transmit the disease than older teenagers and young adults. Scientists aren’t entirely sure why, but one theory is that it has something to do with the way the virus docks with our cells. Coronaviruses are covered by a halo of spike-shaped proteins (that’s where the name comes from: corona, as in crown). These spikes are thought to attach to another protein on the surface of our cells called ACE2. Children have lower levels of ACE2 in their nasal tissue than adults do. That suggests that, under this theory, kids would provide fewer open ports for the virus to dock, invade, and ransack the rest of the body.

Overall, school cases are a reflection of their environment. If COVID-19 is running rampant through your town and you throw a bunch of kids and adults into a building without any safety protocols, the odds are pretty high that you’re going to exacerbate an outbreak. But as cases fall across the country we have to adjust the risk calculus. The choice before us is not between “Keep the schools closed until COVID-19 is eliminated, smallpox-style, from the face of the Earth” and “Open every school immediately.”