Severe Flu Season Predicted With Higher Hospitalizations

Scientists warn against a severe upcoming flu season and a continued possibility of a twindemic, in which COVID-19 and flu epidemics overwhelm hospitals.

After a near lack of a 2020-2021 flu season, the 2021-2022 flu season is expected to be more severe than average. Children are expected to be particularly hard hit this flu season.

Scientists from the University of Pittsburgh Graduate School of Public Health published 2 studies that suggest flu-related hospitalizations and deaths may be mitigated with vaccination rates that are 20% to 50% higher than in previous flu seasons.

“As COVID-19 containment measures—such as masking, distancing and school closures—are relaxed around the world, we’re seeing a fierce resurgence of other respiratory viruses, which does not bode well for the coming flu season,” Mark Roberts, MD, MPP, director of the Public Health Dynamics Laboratory at Pitt Public Health and senior author on both studies, said in a statement. “In a worst-case situation with a highly transmissible flu strain dominating and low influenza vaccination uptake, our predictive models indicate the potential for up to nearly half a million more flu hospitalizations this winter, compared to a normal flu season.”

The Framework for Reconstructing Epidemiologic Dynamics simulation platform found that there could be 20% more flu cases during the 2021-2022 flu season than normal. About half of Americans were vaccinated against the flu during the 2019-2020flu season, and the simulation showed that increasing vaccinations by about 10% resulted in hospitalizations decreasing by 6% to 46% depending how transmissible the dominant flu virus is.

The Susceptible-Exposed-Infected-Recovered model found that there will be 600,000 hospitalizations this upcoming flu season, which is at least 100,000 more than a normal flu season. If vaccine uptake is low, there could be 400,000 more hospitalizations than usual. The model found that 75% of Americans need to be vaccinated against the flu compared with the typical 50%.

The mild flu season in 2020-2021 resulted in waning population-level immunity to influenza, and continued COVID-19 precautions could result in another blunted flu season, which would further erode natural immunity against the flu. In the future, there could be an even larger flu outbreak with higher hospitalizations as social activity returns to normal.

“The ‘twindemic’—a coinciding flu and COVID-19 epidemic—overwhelming our hospitals was thankfully avoided last year. But that does not mean it is no longer possible,” Roberts said. “If anything, our models show that we should be more concerned this year about the possibility of a surge in COVID-19 hitting at the same time as a massive flu outbreak in areas of the country with low vaccination rates against both diseases.”