Flu Season Wrap-Up: Vaccine Effectiveness Low
As the flu season in the U.S. comes to a close, health officials report that this year’s flu vaccine has been notably ineffective, recording one of the lowest effectiveness rates in over a decade.
A new strain of the virus that emerged early in the winter was not well-aligned with the vaccine, resulting in a significant early surge of flu cases.
The Centers for Disease Control and Prevention (CDC) released data indicating a steady decrease in flu-related doctor visits and hospital admissions leading up to last week. The number of states experiencing high flu activity has dropped to 16, primarily in a belt from Colorado to Virginia.
“We’re all thankful that the winter respiratory virus season is winding down,” commented Dr. William Schaffner, a vaccine expert from Vanderbilt University.
The vaccines this season were about 25% to 30% effective in keeping adults from becoming severely ill enough to seek medical treatment, according to a recent CDC report. For vaccinated children, the rate was approximately 40% less likely to require medical attention.
Generally, a flu vaccine is considered satisfactory if it achieves 40% to 60% effectiveness. Based on past CDC studies, this year’s effectiveness appears to be among the lowest in two decades.
The number of flu cases surged in late December, particularly intense in some regions, with New York City officials describing it as the most severe season in 20 years.
Low vaccination rates may have contributed to the situation, but experts also attribute the rise in infections to the new strain responsible for most cases.
This new flu variant falls into the A H3N2 category, specifically subclade K, and seems to spread more effectively, although it doesn’t necessarily lead to more severe illness.
The current vaccine was designed to target a different version of H3N2, so the emergence of this new strain is likely a significant factor behind its diminished effectiveness, according to Schaffner.
CDC estimates indicate that so far this flu season, there have been at least 27 million infections, 350,000 hospitalizations, and around 22,000 deaths attributed to the flu. In comparison, at the same time last year, figures were estimated at over 40 million infections and 520,000 hospitalizations, with a similar death toll.
Sadly, at least 101 children have died this season, with around 85% of those with known vaccination status being unvaccinated against the flu.
While the flu vaccine may not prevent illness in everyone, it is effective in reducing severe cases and fatalities, making it a worthwhile option for protection, according to Schaffner.
CDC data indicates a slight increase in adult vaccination rates this season, now at 46.5%, following a particularly severe flu season last year that resulted in record child deaths this century.
Approximately 48% of children in the U.S. were vaccinated against the flu by the end of last month. This percentage remains stable compared to last year but is down from 52% at this time in 2024, as per CDC reports.
Since 2010, the government has recommended annual flu vaccinations for those aged six months and older. However, in January, the Trump administration shifted this guidance, leaving it to parents and family physicians to determine the best course of action regarding flu shots for children.
Looking ahead, preparations for the next flu season are already underway. Last month, the World Health Organization (WHO) announced recommendations for virus strains that should be targeted in the vaccines for the 2026-27 northern hemisphere flu season. This new guidance includes a focus on subclade K. This week, a U.S. Food and Drug Administration advisory committee backed these WHO recommendations.
