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.
View the full report here.
