Based upon the assumption “that the number of asymptomatic or minimally symptomatic cases is several times as high as the number of reported cases,” experts at the National Institute of Allergy and Infectious Diseases are predicting that Covid-19’s case fatality rate may be considerably less than 1 percent. While that is higher than the rate for seasonal flu (0.1 percent), it’s much lower than the staggering rate we saw in the 1918 influenza pandemic (2.5 percent in the United States, and in some nations higher). It may even fall lower once we have a better sense of the number of mild cases. If this happens and most cases of Covid-19 turn out to be no worse than a nasty but not deadly bout of flu, NPIs like school closings won’t be necessary.

But this kind of data might not be available for analysis until Covid-19 has already spread widely. So for now, policies to contain it should be influenced by the adage “better safe than sorry.” There’s no room for the public to grouse about calls made too early.

After all, it’s easy to reopen schools if the news is good. For example, my colleagues and I observed the use of school closings and other NPIs during the 2009 H1N1 influenza epidemic. During the first days of the outbreak in Mexico, the Health Ministry conducted a broad-based and exacting group of NPIs, similar to the ones we found worked in 1918. The measures appeared to contain the spread of influenza but were revoked 18 days later after it became clear that the H1N1 influenza virus was widespread but not all that deadly.

On the other hand, we studied the use of 559 school closings in Michigan during the fall wave of the 2009 H1N1 influenza epidemic. Eighty-three percent of those closings occurred long after the virus had reached its peak week of infection and had already spread widely among people living in those school districts. The results were all too predictable: The late, reactive school closings had little effect on levels of influenza-like illnesses.

There’s no reason to close schools in communities that have not yet seen Covid-19. But that situation could change quickly, and when it does, school officials, public health agencies and municipal leaders will need to be ready to make the tough call of shutting the schools down. School officials should be checking C.D.C. guidance daily, if not hourly.

In another study, my colleagues and I looked at the spring wave of the 2009 H1N1 influenza epidemic across the United States and found that because of confusion over the advice given by the C.D.C., many school districts closed too late or did not close at all. And of course, when the flu came to these towns, it did what an influenza virus always does: It spread. Good, frequent communication among decision makers will be crucial to avoiding this kind of mishap.

In the meantime, employers ought to develop policies allowing parents to stay at home with their children and not be penalized.