This Year’s Flu Shot Shows Poor Results, Health Officials Report

Federal health authorities report this flu season's vaccine achieved only 25-30% effectiveness in adults, marking one of the worst performance rates in over a decade. A new flu strain that wasn't well-matched to the vaccine caused an intense early wave of infections across the country.

As this year’s influenza season begins to fade, federal health authorities report disappointing news about vaccine performance, with effectiveness rates among the poorest seen in more than ten years.

Health officials point to a new variant that became the dominant strain during early winter months, which poorly matched the available vaccine formulation, resulting in a severe early wave of flu cases nationwide.

Data released Friday by the Centers for Disease Control and Prevention shows continued decreases in medical visits for flu-related symptoms through the previous week. The count of states experiencing high influenza activity fell to 16, with many located in a corridor extending from Colorado through Virginia.

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

According to CDC findings released this week, this season’s immunizations provided approximately 25% to 30% protection against flu severe enough to require medical attention at doctors’ offices, clinics, or hospitals for adults. Vaccinated children showed roughly 40% reduced likelihood of needing medical treatment at healthcare facilities.

Health authorities typically consider flu vaccines successful when they achieve 40% to 60% effectiveness. Based on previous CDC studies, this season recorded among the lowest protection rates witnessed over the past twenty years.

Influenza cases spiked dramatically in late December, hitting certain regions particularly hard. New York City health departments characterized it as the most severe season experienced in two decades.

While relatively modest flu vaccination coverage contributed to the problem, specialists primarily attributed the situation to the emerging flu variant responsible for most infections.

This new variant falls under the A H3N2 category of influenza virus. The specific version, known as subclade K, appeared to transmit more readily, though it didn’t necessarily produce more serious symptoms.

This season’s available vaccine targeted a different H3N2 version, and the rapid spread of the new variant likely explains the reduced vaccine effectiveness, according to Schaffner.

CDC researchers calculate at least 27 million cases, 350,000 hospital admissions, and 22,000 deaths from influenza during this season so far. Comparable figures from the previous year showed at least 40 million illnesses, 520,000 hospitalizations, but similar death totals.

At least 101 children have died this season. Among those with known vaccination records, approximately 85% had not received complete flu immunization.

While flu vaccines may not prevent all illness, they can reduce severity and prevent deaths, making vaccination still valuable, Schaffner emphasized.

CDC information indicates adult vaccination rates increased slightly this season to 46.5%, following last year’s particularly harsh season that established a record for pediatric deaths this century.

Roughly 48% of American children received flu vaccination by late last month. This matches last year’s rate but represents a decline from the 52% vaccinated at the same time in 2024, CDC data shows.

Beginning in 2010, federal authorities recommended yearly flu shots for Americans six months and older. However, in January, the Trump administration discontinued universal flu shot recommendations for all children, stating decisions should rest with parents and family physicians.

Meanwhile, preparations for next winter’s flu season have already begun. Last month, the World Health Organization issued recommendations for virus strains to target in vaccines for the 2026-27 northern hemisphere flu season. The organization specified that vaccines should address subclade K. This week, a U.S. Food and Drug Administration advisory panel supported the WHO guidance.