US Flu Vaccine Shows Poor Effectiveness in 2025-26 Season, Officials Report
As the US flu season draws to a close, health officials have revealed that the flu vaccine performed poorly, marking one of its worst effectiveness rates in more than a decade. According to data released by the Centers for Disease Control and Prevention (CDC), the vaccine's limited success was largely due to a new strain that dominated early winter and was not well-matched to the vaccine formulation.
Low Effectiveness Rates and Impact
The CDC report this week indicated that this season's vaccines were only around 25% to 30% effective in preventing adults from becoming sick enough to require medical attention at a doctor's office, clinic, or hospital. For children, the vaccine offered better protection, with vaccinated children about 40% less likely to need treatment at a healthcare facility. Officials typically aim for flu vaccine effectiveness between 40% and 60%, making this season's performance notably subpar. Based on past CDC research, this represents one of the lowest effectiveness rates in the last two decades.
Surge in Infections and New Strain
Flu infections surged in late December, with some regions experiencing especially intense outbreaks. New York City health officials described it as the most intense flu season in 20 years. The primary culprit was a new flu strain belonging to the A H3N2 category, specifically subclade K, which spread more easily than previous versions. Although it did not necessarily cause more severe illness, its rapid transmission contributed to the vaccine's reduced efficacy. The vaccine available for this season was designed to target a different version of H3N2, leaving it ill-equipped to combat the emerging strain.
Vaccination Rates and Public Health Impact
Relatively low flu vaccination rates exacerbated the situation. CDC data shows adult vaccination rates increased slightly to 46.5% this season, following an unusually severe previous season that set a record for child deaths this century. However, only an estimated 48% of US children were vaccinated against flu by the end of last month, similar to last year but down from 52% at the same point in 2024. Alarmingly, about 85% of the at least 101 children who died this season were not fully vaccinated against flu.
CDC Estimates and Recommendations
CDC scientists estimate there have been at least 27 million illnesses, 350,000 hospitalizations, and 22,000 deaths from flu so far this season. In comparison, at the same point last year, estimates were at least 40 million illnesses and 520,000 hospitalizations, with a similar number of deaths. Despite the vaccine's limitations, experts like Dr. William Schaffner, a Vanderbilt University vaccine expert, emphasize that flu shots remain worthwhile as they can prevent severe illness and death. He noted, "The winter respiratory virus season is slowly coming to a close, and we’re all very grateful for that."
Policy Changes and Future Preparations
In a policy shift, the Trump administration stopped broadly recommending flu shots for all children in January, instead leaving the decision to parents and family doctors. This change comes after the government had recommended annual flu vaccinations for Americans aged 6 months and older since 2010. Meanwhile, preparations for next winter's flu season are already underway. Last month, the World Health Organization recommended including subclade K in vaccines for the 2026-27 northern hemisphere flu season, a move endorsed this week by a US Food and Drug Administration advisory committee.
As the season winds down, the number of states reporting high flu activity has dropped to 16, many in a belt stretching from Colorado to Virginia. The CDC data shows a continued decline in doctor's office and hospital visits for flu symptoms through last week, offering a respite from the intense early onslaught.
