Study details and key findings

For the study, researchers compared the health records of 10,985 patients who were hospitalized with influenza from 2015 and 2019 and 81,280 patients who were hospitalized with COVID-19 from 2020 and 2022. Almost all of the patients were men, and the average age was 71. All data was taken from the U.S. Department of Veterans Affairs.

Overall, the researchers found that both groups had an increased risk of death, hospital readmission, and health problems in different organs, including the brain, heart, and kidneys, after 18 months of follow-up. There were around 615 long-term health issues per 100 people in the COVID-19 group and 537 per 100 people in the influenza group.

However, COVID-19 patients had more severe outcomes than flu patients overall. COVID-19 patients had an increased risk of 64 health problems compared to only six among flu patients, many of which were related to the respiratory or cardiovascular systems. COVID-19 patients were also more likely to die during the study period.

"Many people think they're over Covid-19 or the flu after being discharged from the hospital. That may be true for some people. But our research shows that both viruses can cause long-haul illness," said Ziyad Al-Aly, chief of research and development at the VA St. Louis Health Care System and a clinical epidemiologist at Washington University in St. Louis. "Conceptualising these diseases as acute illnesses is really just looking at the tip of the iceberg, and eclipses the much higher toll of adverse health outcomes that are happening in the post-acute phase."

Commentary

According to Al-Aly, the study's findings suggest that researchers and healthcare providers need to consider viruses in a different light.

"Before the pandemic, I trivialized infections. [I thought] you get sick for a day or two or three, and then you bounce back, and it's all over," Al-Aly said. However, "… [o]ur conception of these illnesses as acute events that you deal with and then put behind you has changed."

"The acute phase is like the tip of an iceberg," he added. "People who get these infections may need attention beyond the acute phase. We need to ask if they have fully recovered, if they are able to go to the gym like before, if they have the same mental acuity."

Other research has also uncovered similar findings. For example, a 2022 study of patients with different respiratory illnesses found that around half of those who were sick with something other than COVID-19 still had lingering issues three months later. Doctors have also reported similar long-term symptoms in patients infected with different respiratory viruses.

"Many have symptoms if they push themselves," said Todd Rice, a professor of medicine in the division of allergy, pulmonary and critical care medicine and director of the medical intensive care unit at the Vanderbilt University Medical Center. "If they used to be able to run 5 miles, now they become short of breath and can only run 3."

Overall, Anita Gupta, an adjunct assistant professor of anesthesiology, critical care and pain medicine at the Johns Hopkins University School of Medicine, praised the new research, saying that it's "a very high-impact study that highlights the gravity of these conditions and the importance of preventing infection with these viruses." (Ducharme, TIME, 12/14; Carroll, NBC News, 12/14; Geddes, The Guardian, 12/14)

As winter approaches, a host of illnesses — including colds, the flu, and strep throat — are becoming more common. Writing for the New York Times, Dana Smith outlines everything you need to know about eight common illnesses, including how long you're contagious with them.