A decision-making guide developed by the national hospice group, based on early data from China, points out that the Covid-19 mortality rate rises with age through the 60s and 70s; it tops 20 percent among people in their 80s who have tested positive. According to the Centers for Disease Control and Prevention, close to 80 percent of early coronavirus deaths occurred among those over 65.

That’s partly because most older adults have chronic conditions — heart or lung disease, diabetes, high blood pressure — known to intensify the virus’s effects. And they have less physiologic reserve — “less ability to rebound from an overwhelming illness,” Dr. White explained.

When seniors and their families engage in what’s called advance-care planning, they often focus on the D.N.R. question — whether patients would want to be resuscitated after cardiac arrest.

But because Covid-19 is a respiratory disease, the more pressing question will likely be whether a hospitalized patient who’s seriously ill will accept intubation and ventilation.

That initially involves a tube inserted down the throat, connected to a ventilator that pushes air into the lungs. When a patient has spent two weeks on a vent, doctors commonly perform a tracheostomy, creating a surgical opening in the windpipe that replaces the swallowed tube.

Long before the virus erupted, among people over 66 who spent 14 days in an I.C.U. on a ventilator, 40 percent died within a year of discharge. Now, “those numbers are too rosy for Covid,” Dr. White said, citing findings from Italy and Britain, where more than half of older patients on prolonged ventilation died.

A just-published JAMA article looked at coronavirus patients admitted to Northwell Health hospitals in and around New York City. Excluding those still hospitalized after the monthlong study, the mortality rate among patients over age 65 exceeded 26 percent, and almost all patients over 65 who needed mechanical ventilation during that period died.