ATLANTA — With the next flu season fast approaching, public health officials are delivering a reassuring message regarding the 2025-2026 influenza campaign. Two separate surveillance reports published on August 8, 2026, have confirmed that the seasonal flu shot provided meaningful protection against the virus, even during a period dominated by antigenically drifted strains of influenza A(H3N2) and influenza B.

Drifted Strains, Defended Populations

The 2025-2026 season presented a unique challenge for prophylactic medicine. According to the CDC, 88% of subtyped influenza A viruses were A(H3N2), and 93% of genetically characterized A(H3N2) samples belonged to subclade K, a subclade that drifted significantly from the specific strain included in the vaccine formulation. Among sequenced influenza B viruses, 64% were clade C.3.1, which also differs from the vaccine strain. Despite this viral mismatch, the data overwhelmingly supports the continued efficacy of vaccination.

The National and State Data

In a sweeping national analysis published in the MMWR Morbidity and Mortality Weekly Report, CDC researchers evaluated vaccine effectiveness (VE) using data from three surveillance networks across 16 U.S. states from September 2025 through February 2026. The study, encompassing 142,494 individuals, found that among children and adolescents, VE was 38% to 41% against influenza-associated outpatient visits and an impressive 41% against hospitalization. For adults, effectiveness ranged from 22% to 34% against outpatient visits and held steady at 30% against severe hospitalization.

Corroborating these findings at the state level, the California Department of Public Health (CDPH) analyzed 952,765 influenza test results. Their data revealed an overall VE of 33% against laboratory-confirmed illness, jumping to 47% against influenza B. Children and adolescents under 18 saw a 39% reduction in risk, proving that the vaccine’s strongest protection generally remains anchored in younger demographics.

Official Public Health Guidance

State and federal health departments continue to urge the public not to abandon the vaccine simply because of viral drift. The official guidance from the California Department of Public Health is embedded below.

“Seasonal flu vaccines remain effective at reducing severe illness and hospitalization, and it's not too late to get vaccinated,” said Dr. Erica Pan, CDPH

— California Department of Public Health (@CAPublicHealth) August 8, 2026

As new vaccines remain in development, the prevailing takeaway for the 2025-2026 season is clear: getting the shot still drastically reduces the risk for outpatient visits, laboratory-confirmed illness, and severe hospitalization. Read the full public health report: Infectious Disease Special Edition