You may have never heard of it, but you may have had it. More evidence points to "long flu" being a real phenomenon, with a large study showing symptoms persist at least 4 weeks or more after some people are hospitalized for the flu.
Researchers compared long flu to long COVID-19 and found long flu happened less often and was less severe overall. This difference could be because the flu (also known as influenza) mostly affects the lungs whereas COVID can affect any number of organ systems in the body.
The investigators were surprised that both long flu and long COVID were linked to a greater burden of health loss, compared to either initial infection.
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"I think COVID and long COVID made us realize that infections have long-term consequences, and often the toll of those long-term consequences is much larger than the toll of acute disease," said Ziyad Al-Aly, MD, senior author of the study and chief of research and development at the VA St. Louis Health Care System.
"I know, having studied long COVID for the past 4 years, I should not be surprised. But I am in awe of what these infections can do to the long-term health of affected individuals," said Al-Aly, who is also a clinical epidemiologist at Washington University in St. Louis.
Al-Aly and colleagues Yan Xie, PhD, and Taeyoung Choi, MS, analyzed US Department of Veterans Affairs medical records. They compared 81,280 people hospitalized with COVID to 10,985 people hospitalized with the flu before the COVID pandemic. They checked up to 18 months after initial infections to see who developed long flu or long COVID symptoms.
The study was published online this month in The Lancet Infectious Diseases journal.
It's an interesting study, said Aaron E. Glatt, MD, chairman of the Department of Medicine and a hospital epidemiologist at Mount Sinai South Nassau in Oceanside, NY, who was not part of the research.
"There is a concern with many viruses that you can have long-term consequences," said Glatt, who is also a fellow of the Infectious Diseases Society of America. He said the possibility of long-term symptoms with the flu is not new, "but it's nice to have more data."
People hospitalized with COVID had a 50% higher risk of death during the study period than people hospitalized with the flu. Put another way, for every 100 people admitted to the hospital with COVID, about eight more died than those hospitalized with the flu over the following 18 months. Hospital admissions and admissions to the intensive care unit were also higher in the long COVID group — 20 more people and nine more people, respectively, for every 100 people admitted to the hospital with COVID.
More research is needed, Glatt said. "With many of these viruses, we don't understand what they do to the body." A prospective study to see if antiviral treatments make a difference, for example, would be useful, he noted.
Al-Aly and colleagues would like to do more studies.
"We need to more deeply understand how and why acute infections cause long-term illness," he said, noting that he also wants to investigate ways to prevent and treat the long-term effects.
"Much remains to be done, and we are deeply committed to doing our best to develop those answers."
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