"Long COVID" has become a well-known potential consequence of COVID infection, with symptoms that can last years.
Now it appears that "long flu" is also possible, with some patients developing long-lasting health problems after a severe infection, a new study finds.
"Long flu" isn't as bad as "long COVID," as it doesn't pose nearly as high a risk to all patients, according to the report published Dec. 14 in The Lancet Infectious Diseases journal.
Still, an analysis of more than 92,000 VA hospital patients found that not only does "long flu" exist, but it can be terrible, said senior researcher Dr. Ziyad Al-Aly, a clinical epidemiologist with the Washington University School of Medicine in St. Louis.
Within a year and a half of infection, patients hospitalized for either COVID-19 or the seasonal flu faced an increased risk of death, landing in the hospital again, or suffering a health problem involving one of their organ systems, results show.
"The big answer is that both COVID-19 and the flu led to long-term health problems, and the big aha moment was the realization that the magnitude of long-term health loss eclipsed the problems that these patients endured in the early phase of the infection," Al-Aly said in a university news release.
"Long COVID is much more of a health problem than COVID, and long flu is much more of a health problem than the flu."
For the study, researchers evaluated data from the U.S. Department of Veterans Affairs on more than 81,000 patients hospitalized for COVID-19 and nearly 11,000 patients hospitalized for the flu.
The researchers tracked patients up to 18 months after infection, looking for 94 different adverse health outcomes involving the body's major organ systems.
"Five years ago, it wouldn't have occurred to me to examine the possibility of a 'long flu,'" Al-Aly said. "A major lesson we learned from SARS-CoV-2 is that an infection that initially was thought to only cause brief illness also can lead to chronic disease."
Patients who had COVID-19 faced a 50% higher risk of death than flu patients in the year and a half after their initial infection, researchers found.
That corresponds to about eight more deaths per 100 patients, results show.
COVID patients also had a greater risk of landing back in the hospital than flu patients.
For every 100 people in each group, there were 20 more hospital admissions and nine more ICU admissions for COVID than for flu, researchers said.
Further, COVID posed a risk to more organ systems. It increased the risk of more than two-thirds (64 of 94) of the health problems examined.
By comparison, the flu posed an elevated risk to just six of the 94 potential health problems, mainly in the respiratory system.
"The one notable exception is that the flu poses higher risks to the pulmonary system than COVID-19," Al-Aly said said. "This tells us the flu is truly more of a respiratory virus, like we've all thought for the past 100 years.
"By comparison, COVID-19 is more aggressive and indiscriminate in that it can attack the pulmonary system, but it can also strike any organ system and is more likely to cause fatal or severe conditions involving the heart, brain, kidneys and other organs."
In both diseases, more than half of death and disability occurred in the months after infection, as opposed to the first 30 days, results show.
That means both are more than a short-term health problem, Al-Aly said.
"The idea that COVID-19 or flu are just acute illnesses overlooks their larger long-term effects on human health," Al-Aly said. "Before the pandemic, we tended to belittle most viral infections by regarding them as somewhat inconsequential: 'You'll get sick and get over it in a few days.'
"But we're discovering that is not everyone's experience. Some people are ending up with serious long-term health issues. We need to wake up to this reality and stop trivializing viral infections and understand that they are major drivers of chronic diseases."
These findings highlight the need for vaccination against both COVID and the flu, Al-Aly added.
"Optimizing vaccination uptake must remain a priority for governments and health systems everywhere," Al-Aly said. "This is especially important for vulnerable populations such as the elderly and people who are immunocompromised."