In the early months of the Covid-19 pandemic, when many people who are now still sick were first infected, the common wisdom was that the coronavirus either sent you to an intensive care unit or, more commonly, caused mild symptoms that resolved after two weeks. But when my sister-in-law got infected in March 2020, she was still burning with fever after three weeks, then six, then more. In this newspaper and elsewhere, young and formerly healthy people shared stories about surviving but not recovering. When I interviewed scientists and clinicians about these lingering symptoms in May, most expressed surprise. “That’s unusual,” one said.

It wasn’t. By May 2020, affected patients had already formed support groups thousands strong, coined terms like long Covid and long-hauler and even conducted research on their own communities. Even that March, people with similar illnesses like myalgic encephalomyelitis (also known as chronic fatigue syndrome or M.E./C.F.S.) had warned that the new pathogen would trigger a wave of disability. They knew then what is clear now: People infected by Covid can be pummeled by months or years of debilitating symptoms, including extreme fatigue, cognitive impairment, chest pain, shortness of breath and postexertional malaise — a state in which existing symptoms worsen after even minor physical or mental exertion.