I want to respond to one point in Lauren Shore’s argument for masks in schools (“Mask Wearing While Advocating for Our Kids” The Jewish Link, December 30, 2021): “A small percentage die. Do we not care about the small percentage?” I thought it would be helpful to mathematically define what is meant by a small percentage.

Let’s focus on mask-wearing as protective of others, since for self-protection, everyone can make their own choice. It should be clear that if you are not infected, you cannot infect others, whether or not you are wearing a mask. And if you get sick, you won’t be in school. We are concerned with those two days of infectiousness before showing symptoms.

New Jersey is currently seeing about 250 new cases a day per 100,000 residents, the highest rate yet. Even so, that means the chance of an individual being infected on a given day is 0.25%. Assuming someone was infectious for two days before symptoms or a positive test, let’s say the chance of being infectious on a given day is therefore 0.5%. Let’s also use an estimated reproductive rate (R0) of 2, meaning a COVID-positive student would infect two others in a class of 20, giving a student a 10% chance of being infected by someone else in the class. The CDC estimates a case fatality rate for children under 18 at 0.002%. The rate is similar for vaccinated working-age adults, so we can include teachers. That would give the chance of a child fatally infecting someone else in school on a given day at 0.000001%, or one in 100 million.

If a mask could completely eliminate this chance, you’d have a 1:100M chance of saving a life by wearing a mask for one entire day. But masks are not completely effective. Estimates vary, but some estimate that medical masks offer about 50% filtration, and cloth masks 10-30%. If you had a mask giving only 50% protection, your chances of saving a life by wearing it are 1 in 200 million; at 10%, it goes to 1 in a billion.

I should mention that these numbers are based on statistics since the start of the pandemic. As people acquire natural or vaccine-induced immunity, the chances of both transmission and death continue to drop. Forcing someone who has recently recovered or been vaccinated to wear a mask all day has zero benefit, since we know they are not infectious.

Clearly saving a life is the highest value in Judaism, and if you feel that wearing a mask all day is a costless act with no downsides, then it seems praiseworthy to do so even for a 1 in a billion chance of saving a life. But clearly many do not feel it is costless, hence the debate, so forcing a child to wear a mask for this miniscule benefit does not seem reasonable.

In summary, to answer the question “Do we not care about the small percentage?” The answer is, it depends how small.