Preliminary estimates show the flu vaccine was up to 55% effective at preventing hospitalizations among adults this season, according to a Feb. 27 CDC report.
This season's preliminary estimates come from four flu surveillance systems covering more than 150,000 inpatient and outpatient encounters nationwide between October 2024 and February 2025.
Four notes:
1. The flu vaccine was 41% to 55% effective at preventing hospitalizations among adults this season. For children and adolescents, these figures ranged from 63% to 78%.
2. The flu shot's effectiveness at preventing outpatient visits ranged from 36% to 54% among adults and 32% to 60% among children.
3. Although influenza A(H3N2) viruses -- typically linked to lower vaccine effectiveness -- have circulated more this season, estimates indicate flu shot effectiveness remains in line with the 2023-24 season and other seasons with higher effectiveness over the past 15 years, according to the CDC.
4. Historically, flu shot efficacy rates have ranged from a high of 60% in the 2010-11 season to a low of 10% for the 2004-05 season, when the CDC started tracking this data.