People who have been hospitalised with flu are at an increased risk of longer-term health problems, similar to those with long Covid, data suggests.
While the symptoms associated with such “long flu” appear to be more focused on the lungs than ongoing Covid symptoms, in both cases the risk of death and disability was greater in the months after infection than in the first 30 days.
“It is very clear that long flu is worse than the flu, and long Covid is worse than Covid,” said Dr Ziyad Al-Aly, a clinical epidemiologist at Washington University in St Louis, Missouri, who led the research.
He was motivated to study the phenomenon after observing the scale of long-term illness experienced by people who have recovered from Covid.
“Five years ago, it wouldn’t have occurred to me to examine the possibility of a ‘long flu.’ But one of the major lessons we learned from this pandemic is that a virus we all initially thought could only cause acute disease is leaving millions of people with long Covid, he said. “We wondered whether this could be happening with other things. Could this be happening with the flu, for example?”
To investigate, Al-Aly and colleagues analysed medical records from 81,280 US patients who were hospitalised with Covid and 10,985 who were hospitalised with seasonal influenza, following them for at least 18 months to learn about their risks of death, hospital readmission and 94 different health problems involving the body’s major organ systems.
The research, published in the Lancet Infectious Diseases, found that while Covid patients faced a greater risk of death or hospital readmission in the following 18 months, both infections carried a significant risk of ongoing disability and disease.
In both cases, more than half of death and disability occurred in the months after infection as opposed to the first 30 days. And while the symptoms associated with long flu were more likely to centre on the lungs – for example, shortness of breath or a cough – compared with Covid patients, both groups were at greater risk of fatigue, cardiovascular, gastrointestinal and neurological issues and symptoms associated with other organ systems in the following months.
“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,” Al-Aly said. “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.
“Some people are ending up with serious long-term health issues. We need to wake up to this reality and stop trivialising viral infections and understand that they are major drivers of chronic diseases.”
The study was not designed to identify what proportion of those hospitalised with influenza go on to develop further health problems, or whether certain groups are at higher risk, and this is something the team hope to investigate in the coming months. Also unclear is the extent to which people who get flu but are not hospitalised develop ongoing health issues.
For now, Al-Aly said the most important thing was to try to reduce the risk of being hospitalised from these illnesses, through vaccination and, in the case of Covid, antiviral drugs.