Flu Shot 26% Effective in Seniors

Led by a team from the U.S. Centers for Disease Control and Prevention (CDC), the findings from a study published in the Journal of Infectious Diseases demonstrated the feasibility of assessing seasonal influenza vaccine effectiveness (VE) using linked immunization and laboratory data from public health surveillance systems.

Published on May 13, 2025, among 1,382,142 laboratory reports, 129,253 persons (9%) (129,253) had a positive influenza test result, of whom 415,390 (30%) had documented influenza vaccination ≥14 days before test date. VE against laboratory-confirmed influenza was 41% (95% confidence interval (CI), 40%–42%). VE was 32% (95% CI, 31%-33%) against influenza A, 68% (95% CI, 66%-69%) against influenza B.

Among older adults aged 65 years or more, flu shot VE was 26% (95% CI, 24%–29 %).

The authors wrote, "Differences in viral evolution may contribute to waning vaccine effectiveness or immune escape."

"Age-related factors contributing to lower VE might include diminished adaptive immune response, increased prevalence of comorbidities, and frailty."

They also noted that the flu shot's lower VE estimates with increasing patient age are consistent with a meta-analysis of test-negative studies conducted from 2004 to 2015.

As of May 9, 2025, the U.S. CDC confirmed that seasonal influenza activity for 2024-2025 is declining. And the CDC continues to recommend that everyone ages 6 months and older get an annual flu vaccine as long as influenza viruses are circulating.