Now Available: First U.S. Flu Vaccine Effectiveness Estimates for 2025-2026

[Centers for Disease Control and Prevention]

Preliminary CDC Estimates of How Well 2025-2026 Seasonal Flu Vaccine Worked Available

March 18, 2026

	Influenza (Flu) 2025 - 2026 Flu Season

www.cdc.gov/flu

Seasonal Flu Vaccination Reduced Medical Visits & Hospitalizations CDC data show this season’s U.S. flu vaccines are protecting against flu. Interim Estimates of 2025–2026 Seasonal Influenza Vaccine Effectiveness—United States, September 2025–February 2026 found that flu vaccination reduced the risk of getting sick or being hospitalized with flu by about one-third overall, despite the fact that most influenza viruses spreading this season had changed since vaccine viruses were chosen for influenza vaccine production. CDC continues to recommend flu vaccination as long as influenza viruses are spreading—even when circulating viruses are drifted from the vaccine viruses—because of the likelihood that vaccine will still offer protection.

2025-26 Interim Flu VE Estimates	Seasonal Flu VE Studies	2025-26 Flu Season

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Preliminary vaccine effectiveness (VE) estimates show the 2025-2026 U.S. seasonal flu vaccines reduced the risk of flu-related medical visits and hospitalizations. Even during seasons when VE is lower, flu vaccination has been shown to prevent serious flu outcomes that can result in hospitalizations and deaths. Data from three U.S. surveillance networks found that flu vaccines reduced the risk of flu-related medical visits for all age groups by 24%–36% and reduced flu-related hospitalizations by 31%. Notably, on average protection was highest among children and adolescents. In CDC’s largest VE network (called VISION): Children and adolescents (younger than 18 years) who got a flu vaccine were 38% less likely to visit a doctor because of flu illness and were 48% less likely to be hospitalized with flu. Adults 18-64 years who got a flu vaccine were 36% less likely to have a medical visit due to flu and were 29% less likely to be hospitalized with flu. Adults 65 years and older were 30% less likely to visit a doctor because of flu, and 31% less likely to be hospitalized with flu. Reduced effectiveness in older adults compared to younger adults and children is common due to the immune system weakening with age. Most of the influenza A viruses this flu season were A(H3N2) subclade K viruses, which are antigenically different from A(H3N2) virus chosen for the seasonal flu vaccine. This means that the virus experienced changes making it harder for vaccine-induced antibodies to recognize and fight the (drifted) attacking virus. While lower vaccine effectiveness is not unexpected, and vaccine effectiveness could not be measured in some age groups against some viruses, the current findings underscore that flu vaccination still reduces the risk of flu-related medical visits and hospitalizations overall and that people who get vaccinated against flu are better protected against flu than people who do not get vaccinated. In addition to flu vaccination, flu antiviral medications are recommended as an important public health tool to treat flu, particularly during seasons with lower VE. Flu antivirals are recommended for patients with flu who are hospitalized, have severe illness, or are at higher risk of developing potentially serious flu complications. As of February 22, 2026, fewer than half of U.S. adults and children had reported getting a 2025–2026 flu vaccine. CDC continues to recommend flu vaccination to reduce your risk from flu, especially serious flu illness and hospitalizations.

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