Influenza symptoms can linger like long Covid: Lancet study

People hospitalised with seasonal influenza can suffer long-term, negative health effects, especially involving their lungs and airways, much like the effects of long Covid, according to a study.

The research, published in The Lancet Infectious Diseases journal, compared the viruses that cause COVID-19 and the flu. It shows that in the 18 months after infection, patients hospitalised for either COVID-19 or seasonal influenza faced an increased risk of death, hospital readmission, and health problems in many organ systems.

The time of highest risk was 30 days or later after initial infection, the researchers said.

“The study illustrates the high toll of death and loss of health following hospitalisation with either COVID-19 or seasonal influenza,” said study senior author Ziyad Al-Aly, a clinical epidemiologist at Washington University, US.

“It’s critical to note that the health risks were higher after the first 30 days of infection. Many people think they are 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.

The analysis spanned up to 18 months post-infection and included a comparative evaluation of risks of death, hospital admissions and 94 adverse health outcomes involving the body’s major organ systems.

The novel approach compared the long-term health effects of a vast array of conditions.

“We wanted to know whether and to what degree people with flu also experience long-term health effects,” Al-Aly said.

“The big answer is that both COVID-19 and the flu led to long-term health problems, and the big aha moment was the realisation that the magnitude of long-term health loss eclipsed the problems that these patients endured in the early phase of the infection,” he said.

The overall risk and occurrence of death, hospital admissions, and loss of health in many organ systems are substantially higher among COVID-19 patients than among those who have had seasonal influenza, Al-Aly said.

“The one notable exception is that the flu poses higher risks to the pulmonary system than COVID-19, he said.

The researchers analysed de-identified medical records in a database maintained by the US Department of Veterans Affairs, the country’s largest integrated health-care delivery system.

They evaluated information involving 81,280 patients hospitalised for COVID-19 at some point from March 1, 2020, through June 30, 2022, as well as 10,985 patients hospitalised for seasonal influenza at some point from October 1, 2015, through Feb. 28, 2019.

During the overall 18-month study period, patients who had COVID-19 faced a 50 per cent higher risk of death than those with seasonal influenza, the researchers said.

This corresponded to about eight more deaths per 100 persons in the COVID-19 group than among those with the flu, they added.