“My son kept asking, ‘Is Daddy going to die? Is he going to die today?’” said Clement Chow, 38, a college professor who has changed his Twitter handle to “Clement ‘I beat COVID19’ Chow.” The first Covid-19 patient at the University of Utah’s intensive care unit, he recently received his all-clear. “It was good to be able to tell him no.”

They are sometimes guilt-ridden, about possibly having spread the disease before its existence was widely known, and about recovering when others did not.

“The death toll from our ship is 11,” said Carl Goldman, 67, who spent 29 days in a Nebraska biocontainment unit after being evacuated from the Diamond Princess cruise ship, which in mid-February was home to the highest concentration of coronavirus cases outside of China. “That could have been any one of us.”

In Italy, some public officials have proposed issuing “immunity certificates” that would allow those with antibodies to the virus to move freely and return to work — an ethically fraught concept also under discussion by the White House’s coronavirus task force.