Interim Estimates of 2025–26 Seasonal Influenza Vaccine Effectiveness — United States, September 2025–February 2026

Abstract

In the United States, annual influenza vaccination has been recommended for all persons aged ≥6 months, including during the 2025–26 season. Interim influenza vaccine effectiveness (VE) estimates were calculated for patients with acute respiratory illness–associated outpatient visits and hospitalizations from three U.S. respiratory virus VE networks during the 2025–26 influenza season, using a test-negative case-control design. Among children and adolescents aged <18 years, VE was 38%–41% against influenza outpatient visits and 41% against influenza-associated hospitalization. Among adults aged ≥18 years, VE was 22%–34% against influenza outpatient visits and 30% against influenza-associated hospitalization. Among children and adolescents, VE against influenza A ranged from 37% (against outpatient visits) to 42% (against hospitalization) across settings; among adults, VE against influenza A ranged from 30% (against hospitalization) to 34% (against outpatient visits) across settings. Among children and adolescents, VE against influenza A(H3N2)–associated outpatient visits was 35% and against influenza A(H3N2)–associated hospitalization was 38%. VE against influenza B outpatient visits ranged from 45%–71% among children and adolescents and was 63% among adults. Other estimates of VE were not statistically significant or were not reportable. Although interim influenza VE is lower during the 2025–26 influenza season than it was during recent influenza seasons, these findings demonstrate that influenza vaccination still provides protection against influenza. CDC recommends influenza vaccination; U.S. influenza vaccines remain available for persons aged ≥6 months.

Introduction

CDC estimates that at least 26,000,000 illnesses, 340,000 hospitalizations, and 21,000 deaths resulting from influenza occurred in the United States during October 1, 2025–February 28, 2026. CDC’s Advisory Committee on Immunization Practices has recommended annual seasonal influenza vaccination for all persons aged ≥6 months, including during the 2025–26 influenza season (1). During the 2024–25 influenza season, influenza vaccination prevented an estimated 5 million medical visits, 180,000 hospitalizations, and 12,000 deaths caused by influenza viruses. During the current 2025–26 influenza season, 88% of subtyped influenza A–positive specimens were influenza A(H3N2); among those, 93% of genetically characterized samples were clade 2a.3a.1 subclade K (J.2.4.1), an antigenically drifted influenza virus that was first identified by CDC in June 2025 after selection of the 2025–26 vaccine viruses and that differs from the 2025–26 A(H3N2) influenza vaccine virus (1). Among sequenced influenza B viruses, 64% were clade C.3.1, which also differs antigenically from the 2025–26 influenza B vaccine virus. As of February 21, 2026, an estimated 48% of U.S. children and adolescents aged 6 months–17 years and 47% of U.S. adults aged ≥18 years had received an influenza vaccination during the 2025–26 season. CDC has monitored influenza vaccine effectiveness (VE) since 2004. This report provides interim estimates of 2025–26 influenza VE against outpatient visits and hospitalization for laboratory-confirmed influenza among children, adolescents, and adults from three U.S. surveillance networks.

Methods

Data Source and Collection

Data from three CDC-affiliated surveillance networks were used to assess influenza VE during September 2025–February 2026: 1) the New Vaccine Surveillance Network (NVSN), 2) the U.S. Flu VE Network (U.S. Flu VE), and 3) the Virtual SARS-CoV-2, Influenza, and Other respiratory viruses Network (VISION). Patient ages and care settings differ by network (Box). U.S. Flu VE enrolls only outpatients, NVSN* enrolls both outpatients and inpatients, and VISION retrospectively analyzes medical records of eligible outpatients and inpatients. All three networks include children and adolescents; U.S. Flu VE and VISION also include adults.

Test-negative, case-control designs were used to estimate influenza VE among case-patients and control patients receiving outpatient or inpatient care for an acute respiratory illness (ARI) during the 2025–26 influenza season. ARI definitions varied by network. Case-patients were those with ARI who received a positive influenza virus molecular assay test result,^† and control patients were those with ARI who received a negative influenza virus test result.

Data Analysis

To assess the association between influenza vaccination and influenza-associated outpatient visits or hospitalization, multivariable logistic regression was used. Odds ratios were calculated and adjusted for study site, patient age, date of illness, and other potential confounders.^§ VE was estimated as (1 − adjusted odds ratio) × 100(%). Patients were considered vaccinated if they had received ≥1 dose of any 2025–26 influenza vaccine ≥14 days before the index date (ARI onset or clinical encounter).^¶ Patients were excluded if they were vaccinated <14 days before the index date or had received a positive SARS-CoV-2 molecular test result at the time of testing for influenza** (2).

VE against an outpatient medical encounter and against hospitalization was calculated for any influenza, influenza A and B, and influenza A subtypes (A[H1N1]pdm09 and A[H3N2]) across networks and care settings, when possible. VE point estimates and 95% CIs are included in this report; CIs that exclude zero were considered statistically significant. VE estimates were not reported for strata with sparse data resulting in unstable model estimates, indicated by very wide CIs (range ≥100), even when case count thresholds were met (3).

Analyses were conducted using SAS software (version 9.4; SAS Institute) and R (version 4.5; R Foundation). NVSN and U.S. Flu VE activities were reviewed by CDC, deemed not research, and were conducted consistent with applicable federal law and CDC policy.^†† VISION activities were reviewed by CDC, deemed not research or research not involving human subjects, and were conducted consistent with applicable federal law and CDC policy.^§§

Results

The analysis sample comprised 142,494 persons from all three surveillance networks, including 3,692 (3%) from NVSN, 3,380 (2%) from U.S. Flu VE, and 135,422 (95%) from VISION (Table 1) (Supplementary Table 1). Among the 3,692 children and adolescents aged 6 months–17 years included in NVSN, 2,296 (62%) were enrolled from outpatient settings, and 1,396 (38%) were hospitalized (Table 1). U.S. Flu VE included 3,380 outpatients aged ≥8 months. Among 135,422 VISION encounters for persons aged ≥6 months, 108,539 (80%) were outpatient and 26,883 (20%) were inpatient encounters.

Influenza Vaccination Status

Among patients aged 6 months–17 years (NVSN and VISION) and 8 months–17 years (U.S. Flu VE) evaluated in outpatient settings, 17%–26% of case-patients and 22%–31% of control patients had received an influenza vaccination; among those who were hospitalized, 20%–33% of case-patients and 29%–43% of control patients had received an influenza vaccination (Table 2). Among adults evaluated in outpatient settings, 26%–32% of case-patients and 35%–40% of control patients had been vaccinated. Among those who were hospitalized, 37% of case-patients and 40% of control patients had received an influenza vaccination. Among adults aged ≥65 years evaluated in outpatient settings, 48%–61% of case-patients and 54%–68% of control patients had been vaccinated; 44% of case-patients and 46% of control patients who were hospitalized had received an influenza vaccination.

VE Among Pediatric Patients

Among children and adolescents, VE against an outpatient visit for any influenza ranged from 38% (VISION) to 41% (NVSN); for influenza A, VE ranged from 37% (NVSN) to 38% (VISION); and for influenza B, VE ranged from 45% (VISION) to 71% (NVSN) (Table 2). VE against an outpatient visit for influenza A(H3N2) was 35% (NVSN). In U.S. Flu VE, estimates of VE against an outpatient visit for any influenza (14%), influenza A (10%), influenza A(H3N2) (2%), and influenza B (20%) were not statistically significant. VE against hospitalization for any influenza was 41%, for influenza A was 42%, and for influenza A(H3N2) was 38% (NVSN). In VISION, VE against hospitalization for any influenza and influenza A (48%) was not statistically significant. VE against hospitalization for influenza B was not reportable because of unstable model estimates resulting from sparsity of data.

VE Among Adult Patients

Adults aged ≥18 years. Among all adults aged ≥18 years, influenza VE against an outpatient visit for any influenza ranged from 22% (U.S. Flu VE) to 34% (VISION), for influenza A was 34% (VISION), and for influenza B was 63% (VISION). In U.S. Flu VE, estimates of influenza VE against an outpatient visit for influenza A (21%), influenza A(H3N2) (11%), and influenza B (23%) were not statistically significant. In VISION, influenza VE against hospitalization for any influenza and influenza A was 30%. VE against hospitalization for influenza B was not reportable.

Adults aged 18–64 years. Among adults aged 18–64 years in VISION, influenza VE against an outpatient visit for any influenza was 36%, for influenza A was 35%, and for influenza B was 66%. In U.S. Flu VE, estimates of VE against an outpatient visit for any influenza (24%), influenza A (23%), and influenza A(H3N2) (12%) were not statistically significant. In VISION, VE against hospitalization for any influenza was 29% and for influenza A was 28%. Influenza B VE against outpatient visits (U.S. Flu VE) and hospitalization (VISION) were not reportable.

Adults aged ≥65 years. Among adults aged ≥65 years, influenza VE against an outpatient visit for any influenza ranged from 30% (VISION) to 41% (U.S. Flu VE). VE against an outpatient visit for influenza A was 30% (VISION). In U.S. Flu VE, estimates of VE against an outpatient visit for influenza A (40%) and influenza A(H3N2) (37%) were not statistically significant. VE against hospitalization for any influenza and influenza A was 31% (VISION). VE estimates for influenza B were not reportable.

Genetic Characterization of Influenza Viruses

As of February 18, 2026, a total of 572 influenza A(H3N2) viruses had been genetically characterized at CDC. Subclade K was detected in 474 (83%) samples (Supplementary Table 2) and was antigenically distinct from the 2025–26 A(H3N2) influenza vaccine virus (A/Croatia/10136RV/2023). Among 47 sequenced A(H1N1)pdm09 viruses and 108 sequenced B/Victoria viruses, clades D.3.1 (51%) and C.3.1 (81%) predominated, respectively. The B/Victoria clade C.3.1 differs from the influenza vaccine virus in the 2025–26 influenza season, whereas circulating A(H1N1) pdm09 viruses are similar to the selected vaccine virus (1).

Discussion

Receipt of a 2025–26 seasonal influenza vaccine reduced the risk for influenza-associated outpatient visits (VE = 24%–36%) and influenza-associated hospitalization (VE = 31%) across all age groups. VE against outpatient visits was, on average, highest in children and adolescents (VE = 38%–41%). Protection against influenza-associated hospitalization was also highest in children and adolescents (VE = 41%), whereas VE against hospitalization in adults aged 18–64 years (VE = 29%) and ≥65 years (VE = 31%) was lower. Lower VE among older adults compared with that in younger persons has been observed in past influenza seasons, especially against A(H3N2) viruses (4).

Overall U.S. interim VE estimates against outpatient visits are comparable to estimates from China (24%), Canada (38% [influenza A]), and Europe (37%–40%) (5–7). U.S. interim estimates of VE against hospitalization are also comparable to estimates of VE in hospital settings in Europe (21%–42%) (7).

Sequencing data indicate that most influenza viruses circulating in the United States are A(H3N2) subclade K, an antigenically drifted virus predominant in the current season in most countries with available VE estimates. Lower influenza VE has been observed in some seasons when antigenically drifted viruses have circulated, but influenza vaccines have also been determined to provide protection against drifted viruses in previous recent influenza seasons (4). During the 2018–19 influenza season, a drifted A(H3N2) virus circulated, and an overall VE of 29% was observed (8).

U.S. interim VE estimates against influenza B outpatient visits are higher than estimates from Europe (−10%–35%) (7). VE against influenza B was high in both children and adults, consistent with the 2019–20 influenza season in the United States, during which influenza B viruses circulated and were antigenically drifted from the 2019–20 influenza B vaccine virus (9).

Influenza vaccination reduced the likelihood of both influenza-associated outpatient visits and hospitalizations, even with a circulating influenza A(H3N2) virus that is antigenically drifted from the vaccine virus. These findings support CDC’s recommendation for annual influenza vaccination (1). While influenza viruses continue to circulate, vaccination of eligible persons who have not yet received a 2025–26 influenza vaccine could reduce influenza-associated morbidity and mortality. CDC will continue to monitor influenza VE throughout the 2025–26 influenza season.

Limitations

These findings are subject to at least four limitations. First, VE results are preliminary, and end-of-season estimates might change as influenza continues to spread during the 2025–26 season. Second, because factors such as underlying medical conditions and prior season influenza vaccination status were not modeled, the potential for unmeasured confounding exists. Third, self-reported vaccination data, receipt of vaccinations outside the medical system that were not documented, and the recommendation for administration of 2 influenza vaccine doses for children aged 6 months–8 years the first time they are vaccinated could have resulted in misclassification of vaccination status and biased VE estimates downward. Finally, small sample sizes precluded estimation of VE across all strata and VE against influenza A(H1N1)pdm09. Differences in VE estimates across networks might be the result of differences in ARI case definitions, active versus passive surveillance approaches that determine influenza testing practices and vaccination ascertainment (i.e., inclusion of self-report), outpatient care settings, and underlying site populations.

Implications for Public Health Practice

As of February 21, 2026, fewer than one half of U.S. adults and children had received a 2025–26 influenza vaccine. Influenza vaccination can prevent medically attended illnesses and serious disease that might result in hospitalization or death. Even in seasons when overall VE is reduced, influenza vaccination has prevented thousands of hospitalizations and deaths, as observed in the 2022–23 influenza season when influenza VE was just 30%, yet influenza vaccines prevented an estimated 71,000 hospitalizations and 4,300 deaths. CDC recommends that eligible persons receive influenza vaccination (1); U.S. influenza vaccines remain available for persons aged ≥6 months. Influenza antiviral medications are an additional important public health tool, particularly during seasons with lower VE. Administration of antiviral medication is recommended as soon as possible for any patient with suspected or confirmed influenza who is hospitalized; has severe, complicated, or progressive illness; or is at higher risk for influenza complications. Receipt of a 2025–26 influenza vaccine reduced the risk for influenza-associated outpatient visits and hospitalizations.

CDC Influenza Vaccine Effectiveness Collaborators

Virtual SARS-CoV-2, Influenza, and Other respiratory viruses Network collaborators

Omobosola Akinsete, HealthPartners Institute; Sarah W. Ball, Westat, Inc.; Michelle A. Barron, University of Colorado Anschutz Medical Campus; Daniel Bride, Intermountain Health; Brian E. Dixon, Regenstrief Institute; John Hansen, Kaiser Permanente Northern California; David Mayer, University of Colorado Anschutz Medical Campus; Charlene McEvoy, HealthPartners Institute; Allison L. Naleway, Kaiser Permanente Center for Health Research; Varsha Neelam, National Center for Immunization and Respiratory Diseases, CDC; Caitlin Ray, National Center for Immunization and Respiratory Diseases, CDC; Colin Rogerson, Regenstrief Institute; S. Bianca Salas, Kaiser Permanente Southern California; Tamara Sheffield, Intermountain Health; Lina S. Sy, Kaiser Permanente Southern California; Duck-Hye Yang, Westat, Inc.; Ousseny Zerbo, Kaiser Permanente Northern California.

U.S. Flu Vaccine Effectiveness Network collaborators

Tara Curley, Washington University School of Medicine in St. Louis; Kiran A. Faryar, University Hospitals Cleveland Medical Center; Joanna Kramer, Phoenix Children’s Hospital; Jay Krishnan, University Hospitals Cleveland Medical Center; Taylor Kristicevich, Washington University School of Medicine in St. Louis; Aleda M. Leis, University of Michigan; Amanda McKillop, Baylor Scott & White Health; Lora Nordstrom, Valleywise Health; Leah Odame-Bamfo, Baylor Scott & White Health; Ivana A. Vaughn, Henry Ford Health; Emmanuel B. Walter, Duke Human Vaccine Institute; Elizabeth Wettick, University of Pittsburgh Student Health Services; Brianna M. Wickersham, Kaiser Permanente Washington Health Research Institute; Olivia L. Williams, Duke Human Vaccine Institute; Brian D. Williamson, Kaiser Permanente Washington Health Research Institute; Richard K. Zimmerman, University of Pittsburgh School of Medicine.

New Vaccine Surveillance Network collaborators

Haris M. Ahmad, National Center for Immunization and Respiratory Diseases, CDC; Christina Albertin, University of Rochester School of Medicine and Dentistry; Vasanthi Avadhanula, Baylor College of Medicine and Texas Children’s Hospital; James D. Chappell, Vanderbilt University Medical Center; Juliana DaSilva, National Center for Immunization and Respiratory Diseases, CDC; Janet A. Englund, Seattle Children’s Research Institute; Megan C. Freeman, UPMC Children’s Hospital of Pittsburgh and University of Pittsburgh School of Medicine; Lisa M. Keong, National Center for Immunization and Respiratory Diseases, CDC; Eileen J. Klein, Seattle Children’s Research Institute; Mary E. Moffatt, Children’s Mercy and University of Missouri-Kansas City School of Medicine; Daniel C. Payne, Cincinnati Children’s Hospital Medical Center and University of Cincinnati College of Medicine; Leila C. Sahni, Baylor College of Medicine and Texas Children’s Hospital; Elizabeth P. Schlaudecker, Cincinnati Children’s Hospital Medical Center and University of Cincinnati College of Medicine; Rangaraj Selvarangan, Children’s Mercy and University of Missouri-Kansas City School of Medicine; Laura S. Stewart, Vanderbilt University Medical Center; Peter G. Szilagyi, University of Rochester School of Medicine and Dentistry and UCLA Department of Pediatrics; John V. Williams, UPMC Children’s Hospital of Pittsburgh and University of Pittsburgh School of Medicine and University of Wisconsin School of Medicine and Public Health.