This is not true of infectious scourges such as influenza. The flu hits the elderly and chronically ill hard, too, but it also kills children. Trying to create herd immunity among those most likely to recover from infection while also isolating the young and the old is daunting, to say the least. How does one allow exposure and immunity to develop in parents, without exposing their young children?

The clustering of complications and death from Covid-19 among the elderly and chronically ill, but not children (there have been only very rare deaths in children), suggests that we could achieve the crucial goals of social distancing — saving lives and not overwhelming our medical system — by preferentially protecting the medically frail and those over age 60, and in particular those over 70 and 80, from exposure.

Why does this matter?

I am deeply concerned that the social, economic and public health consequences of this near total meltdown of normal life — schools and businesses closed, gatherings banned — will be long lasting and calamitous, possibly graver than the direct toll of the virus itself. The stock market will bounce back in time, but many businesses never will. The unemployment, impoverishment and despair likely to result will be public health scourges of the first order.

Worse, I fear our efforts will do little to contain the virus, because we have a resource-constrained, fragmented, perennially underfunded public health system. Distributing such limited resources so widely, so shallowly and so haphazardly is a formula for failure. How certain are you of the best ways to protect your most vulnerable loved ones? How readily can you get tested?

We have already failed to respond as decisively as China or South Korea, and lack the means to respond like Singapore. We are following in Italy’s wake, at risk of seeing our medical system overwhelmed twice: First when people rush to get tested for the coronavirus, and again when the especially vulnerable succumb to severe infection and require hospital beds.

Yes, in more and more places we are limiting gatherings uniformly, a tactic I call “horizontal interdiction” — when containment policies are applied to the entire population without consideration of their risk for severe infection.

But as the work force is laid off en masse (our family has one adult child home for that reason already), and colleges close (we have another two young adults back home for this reason), young people of indeterminate infectious status are being sent home to huddle with their families nationwide. And because we lack widespread testing, they may be carrying the virus and transmitting it to their 50-something parents, and 70- or 80-something grandparents. If there are any clear guidelines for behavior within families — what I call “vertical interdiction” — I have not seen them.