Flu vaccines didn’t work that well in the US, officials find

NEW YORK– As the U.S. flu season draws to a close, health officials say the flu vaccine hasn’t worked very well, with one of its worst effectiveness rates in more than a decade.

A new strain that dominated the early winter was not well suited to the vaccine, leading to an intense early attack of influenza.

The Centers for Disease Control and Prevention released data Friday showing a continued decline in doctor and hospital visits for flu symptoms through last week. The number of states reporting high flu activity fell to 16, most of them in a belt stretching from Colorado to Virginia.

“The winter season for respiratory viruses is slowly coming to an end, and we are all very grateful for that,” said Dr. William Schaffner, a vaccine expert at Vanderbilt University.

This season’s vaccines were between 25 and 30 percent effective in preventing adults from getting sick enough from the flu to need to go to a doctor, clinic or hospital, according to a CDC report released this week. Vaccinated children were about 40% less likely to receive treatment in a doctor’s office or hospital.

Authorities are generally satisfied if a flu vaccine is 40 or 60 percent effective. Judging from previous CDC research, this season had one of the lowest efficacy rates in the last two decades.

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

Relatively low flu vaccination rates haven’t helped, but experts have also blamed most infections on the new flu strain.

The new strain belonged to a category of influenza virus, called A H3N2. This new version, subclade K, seemed to spread more easily, although it did not necessarily cause more severe disease.

The vaccine available for this season was designed to fight a different version of H3N2, and the explosion of the new strain is a likely explanation for why the vaccine was less effective, Schaffner said.

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

At least 101 children have died so far this season. Among those with known vaccination status, approximately 85% were not fully vaccinated against influenza.

The flu vaccine may not protect everyone from getting sick, but it can prevent people from getting seriously ill and dying. That’s why it’s always helpful to get a flu shot, Schaffner said.

CDC data suggests that adult vaccination rates rose slightly this season, to 46.5%, after an unusually poor season last year that set a record for the most child deaths this century.

An estimated 48% of American children were vaccinated against the flu as of the end of last month. That’s about the same as last year, but down from 52% vaccinated at this point in 2024, according to CDC data.

Since 2010, the government has recommended annual flu vaccinations for Americans aged 6 months and older. However, in January, the Trump administration stopped widely recommending the flu vaccine to all children, instead saying it was up to parents and family doctors to decide.

Meanwhile, work is already underway for next winter’s flu season. Last month, the World Health Organization announced its recommendations for which virus strains to address in vaccines for the northern hemisphere’s 2026-2027 flu season. Vaccines should be designed to handle the K subclade, the organization said. This week, a U.S. Food and Drug Administration advisory committee endorsed the WHO recommendations.

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