The study found that some of the long Covid patterns related to age, sex, race and ethnicity differed from those seen in deaths caused by the initial infection. For example, while Black and Hispanic people had higher death rates from the initial coronavirus infection than non-Hispanic whites, those groups did not have higher death rates related to long Covid, the study found.

The researchers suggested that the difference might be partly because of systemic disparities that have resulted in less access to health care for Black and Hispanic patients, who might not have received appropriate long-Covid diagnoses. The study said it was also possible that, because Black and Hispanic patients died at higher rates from the initial illness than white patients, they might have “fewer Covid-19 survivors left to experience long-Covid conditions.”

Nearly 57 percent of deaths related to long Covid were in people 75 and older. Nearly a third of the death certificates that mentioned long Covid listed the underlying or main cause of death as a non-Covid condition such as heart disease, cancer or Alzheimer’s.

“This is just scratching the surface — this is a first look,” said David Putrino, the director of rehabilitation innovation for the Mount Sinai Health System in New York, who was not involved in the study.

He said the study appeared to be primarily capturing deaths of people who experienced serious initial infection with the coronavirus and who survived that phase but went on to have organ damage and other severe complications. He said other deaths related to long Covid should be studied, including deaths by suicide of people who had devastating post-Covid symptoms.

Another report published on Wednesday, by the Documenting Covid-19 project, offered a snapshot of deaths related to long Covid by looking at death certificates in 2020 and 2021 in Minnesota, New Mexico and a few other locations. That report, conducted by the Brown Institute for Media Innovation at Columbia University and MuckRock, a public records foundation, found that 18 of the 28 deaths associated with long Covid in Minnesota during those years were in people over 80 years old and that most of the patients had worked in blue-collar jobs and lacked a college degree. In New Mexico, about a third of the 13 deaths related to long Covid were in people under 60, and some were frontline or essential workers, the report said.

Experts evaluating the C.D.C. study cautioned that it was both an incomplete picture of mortality linked to long Covid and of the larger toll of the condition, which has been estimated by the Government Accountability Office to have affected 7.7 million to 23 million people in the United States.

“This is an important thing to explore and study, but it shouldn’t be used as a proxy for saying, Oh, well, long Covid isn’t that severe because look how few deaths there are,” Dr. Putrino said. “We should not be measuring the damage that long Covid does by deaths alone.”