Health officials say the 2025-26 U.S. flu season is ending more slowly than some residents may have expected, even as doctor’s office and hospital visits for flu symptoms declined in recent weeks. In the latest CDC data released as the season wound down, officials reported a continued drop in flu activity, including fewer states with high flu levels, but they also said the vaccine did not perform well this year.
The CDC posted data showing a decline through last week in doctor’s office and hospital visits for flu symptoms, and it also said the number of states reporting high flu activity fell to 16. The early part of the season was marked by an intense surge in late December, when health officials said the virus spread quickly in multiple regions.
Health experts said this season’s vaccine mismatch played a key role. Dr. William Schaffner, a Vanderbilt University vaccine expert, said officials were “very grateful” the respiratory virus season was “slowly coming to a close,” and he pointed to the match between circulating strains and what the vaccine was designed to cover as an explanation for the season’s weak vaccine performance.
A CDC report this week estimated the current flu vaccines were around 25% to 30% effective in preventing adults from becoming sick enough from the flu to need treatment in a doctor’s office, clinic or hospital. For children who were vaccinated, the CDC report estimated vaccinated children were about 40% less likely to get treatment at a doctor’s office or hospital, a protection level officials said remains meaningful even when overall effectiveness is low.
Officials said vaccine effectiveness is generally considered acceptable when it reaches roughly 40% to 60% and that, based on past CDC research, the season marked one of the lowest effectiveness rates in the last two decades. They attributed much of the poor performance to a new flu strain that dominated early winter and was not well matched by the vaccine.
The strain belonged to the H3N2 influenza category, but officials said it was a subclade K version that spread more easily than earlier forms. Schaffner said the vaccine available for the season was built to address a different version of H3N2, and he described the explosive spread of subclade K as a likely reason the vaccine was less effective than usual.
CDC scientists estimated that, so far this season, there have been at least 27 million illnesses, 350,000 hospitalizations and 22,000 deaths from flu. At the same point last year, CDC estimated at least 40 million illnesses and 520,000 hospitalizations, while the number of deaths was about the same, according to the report cited by AP.
The CDC data also showed the toll on children, with at least 101 child deaths so far this season. For children whose vaccination status was known, officials said about 85% were not fully vaccinated against flu.
Even with the weak match, Schaffner emphasized that flu shots still matter because they may help prevent people from severe illness and death. Officials said CDC data also suggested adult vaccination rates were up slightly this season to 46.5%, following an unusually bad season last year. They reported that about 48% of U.S. kids were vaccinated around the end of last month, about the same as last year but below a higher level at the same point in 2024.
Looking ahead, officials said work for next winter’s vaccine is already under way. The World Health Organization announced recommendations in January for which virus strains should be targeted in vaccines for the 2026-27 northern hemisphere season, and it said vaccines should be built to handle subclade K; a U.S. Food and Drug Administration advisory committee endorsed those WHO recommendations this week.