CDC Reports Interim 2025-26 Influenza Vaccine Effectiveness

Key Takeaways

• Vaccination was associated with reduced risk for influenza-associated outpatient visits and hospitalization, with higher overall estimates in children and adolescents than in adults.
• Reported protection included influenza A(H3N2) and influenza B, although some subgroup and subtype estimates were not statistically significant or could not be reported.
• The findings were interim, and CDC reiterated its vaccination recommendation, noted vaccine availability for people aged 6 months and older, and described antivirals as an additional public health tool.

Interim U.S. estimates linked 2025–26 influenza vaccination with lower risk for laboratory-confirmed influenza encounters, with pediatric outpatient effectiveness reaching 41% in the March 12, 2026 MMWR report. Adult estimates were lower across outpatient and hospital settings. The analysis focused on medically attended illness rather than community infections and used laboratory confirmation to define cases. It covered outpatient visits and hospitalization outcomes across three national surveillance networks.

Researchers used a test-negative case-control design and multivariable logistic regression to estimate vaccine effectiveness from September 2025 through February 2026. Data came from 142,494 patients in CDC-affiliated surveillance networks, including 3,692 in NVSN, 3,380 in U.S. Flu VE, and 135,422 in VISION. Network-specific inclusion periods were September 20, 2025, to February 6, 2026, in NVSN; September 28, 2025, to January 23, 2026, in U.S. Flu VE; and October 1, 2025, to January 23, 2026, in VISION. Participants included children and adolescents aged 6 months to 17 years in NVSN and VISION, children and adolescents aged 8 months to 17 years in U.S. Flu VE, and adults aged 18 years and older in U.S. Flu VE and VISION, all with acute respiratory illness. They were evaluated in outpatient clinics, urgent care, emergency departments, or hospitals, and estimates compared vaccinated with unvaccinated patients across those settings.

Among children and adolescents, effectiveness against influenza-associated outpatient visits for any influenza ranged from 38% to 41%, and effectiveness against hospitalization was 41%. Among adults aged 18 years and older, outpatient effectiveness ranged from 22% to 34%, and hospitalization effectiveness was 30%. In adults aged 18 to 64 years, outpatient estimates were 36% in VISION and 24% in U.S. Flu VE, although the U.S. Flu VE estimate was not statistically significant, with hospitalization effectiveness of 29% in VISION. Among adults aged 65 years and older, outpatient estimates ranged from 30% to 41%, and hospitalization effectiveness was 31% in VISION. Across outcomes, overall estimates were highest in younger patients.

Subtype analyses showed 35% effectiveness against influenza A(H3N2) outpatient visits and 38% against hospitalization among children and adolescents. For influenza B outpatient visits, effectiveness ranged from 45% to 71% in children and adolescents and was 63% in adults. Effectiveness against influenza A(H1N1)pdm09 could not be estimated because small sample sizes limited analysis across strata. Some subgroup and subtype estimates were not statistically significant or were not reportable, leaving precision uneven across age groups and networks.

CDC described the estimates as preliminary and noted they could change as the season continues. The authors cited potential unmeasured confounding, possible vaccination-status misclassification, sparse data, and network differences in illness definitions, surveillance approaches, settings, and populations. They also noted that some outpatient participants in NVSN might later have required higher-level care that was not captured. CDC said the findings support its annual vaccination recommendation, noted that vaccines remained available for people aged 6 months and older, and described antivirals as an additional tool. Overall, the interim estimates showed measurable but uneven protection across outcomes, age groups, and virus types during the 2025–26 season.