U.S. Flu Season Winding Down

The CDC on Friday posted data that showed a continued decline in doctor’s office and hospital visits for flu symptoms through last week. The number of states reporting high flu activity dropped to 16, many of them in a belt stretching from Colorado to Virginia.

“The winter respiratory virus season is slowly coming to a close, and we’re all very grateful for that,” said William Schaffner, MD, a Vanderbilt University vaccine expert.

CDC scientists estimate there have been at least 27 million illnesses, 350,000 hospitalizations, and 22,000 deaths from flu so far this season. At the same point last year, the estimates were at least 40 million illnesses, 520,000 hospitalizations, but about the same number of deaths.

Flu infections surged in late December and were especially intense in some parts of the country. New York City health officials called it the most intense season in 20 years.

At least 101 children have died so far this season, down from the unusually bad season in 2024-2025 that set a record for the most child flu deaths this century with more than 200. For those whose vaccination status is known this season, about 85% were not fully vaccinated against the flu.

The flu vaccine may not protect everyone from getting sick, but it can prevent people from becoming severely ill and dying. That’s why getting a flu shot remains worthwhile, Schaffner said.

Relatively low flu vaccination rates did not help this season, but experts also blamed a new flu strain that was not well matched to the vaccine for causing most infections.

The new strain, A H3N2 subclade K, seemed to spread more easily — though it did not necessarily cause more severe illness.

The vaccine available for this season was built to address a different version of H3N2. Next year’s should be built to handle subclade K, following recommendations last month from the World Health Organization and the FDA’s vaccine advisors on Thursday.

The new strain’s explosion is a likely explanation for why the vaccine was less effective, Schaffner said.

This season’s vaccines were around 25% to 30% effective in preventing adults from getting sick enough from the flu that they had to go to a doctor’s office, clinic, or hospital, according to CDC reports this week. Children who were vaccinated were about 40% less likely to get treatment at a doctor’s office or hospital.

Officials generally are pleased if a flu vaccine is 40% to 60% effective. Judging from past CDC research, this season saw one of the lowest effectiveness rates in the last two decades.

Starting in 2010, the government recommended annual flu vaccinations for Americans 6 months and older. In January, however, the Trump administration stopped broadly recommending flu shots for all children, saying instead that it’s up to parents and family doctors to decide.

CDC data suggest adult vaccination rates are up slightly this season, to 46.5%. An estimated 48% of U.S. kids were vaccinated against flu around the end of last month. That’s about the same as last year, but down from the 52% vaccinated at this point in 2024, according to CDC data.