In this week’s CDC Morbidity and Mortality Weekly Report, investigators characterize the 2024 to 2025 U.S. influenza season as high severity with co-circulation of A(H1N1)pdm09 and A(H3N2). Using FluSurv-NET, which covers about 9 percent of the U.S. population, the cumulative influenza-associated hospitalization rate from October 1, 2024, through April 30, 2025 was 127.1 per 100,000, the highest observed since 2010 to 2011.1
Hospitalization rates were elevated across all age groups, ranging from 1.8 to 2.8 times higher than median historical rates. Adults aged 75 years or older had the highest burden at 598.8 per 100,000. In-hospital severity indicators were similar to prior seasons: 16.8 percent of patients were admitted to an intensive care unit, 6.1 percent received invasive mechanical ventilation, and 3.0 percent died during hospitalization. Underlying medical conditions were present in 89.1 percent of hospitalized patients.1
Investigators noted, “Season severity appears driven by higher incidence rather than unusual clinical severity, with hospitalized patients resembling prior seasons’ risk profiles and resource needs. Despite recommendations, inpatient antiviral use remains suboptimal, particularly among school-aged children, highlighting the need for timely treatment alongside vaccination and basic prevention.”1
What You Need To Know
Hospitalization burden exceeded prior FluSurv-NET seasons across all age groups, with the highest rates in adults 75 years and older while ICU and ventilation proportions were similar to past years.
About one third of hospitalized patients had been vaccinated and antiviral use was lowest among children 5 to 17 years, indicating opportunities to improve timely treatment.
Estimates are preliminary from a 9 percent US catchment with frequent missing subtype data, so clinicians should interpret cautiously while reinforcing vaccination and prompt antivirals for hospitalized patients.
Vaccination coverage among hospitalized patients was 32.4 percent. Antiviral therapy was administered to 84.8 percent of patients, with the lowest treatment proportion in those aged 5 to 17 years at 61.6 percent. These findings indicate the largest hospitalization burden in the FluSurv-NET era while ICU and ventilation proportions remained stable.1
Interpretation is subject to several limitations. Testing is clinician-driven and may underestimate hospitalization rates. Influenza A subtype was frequently missing and required imputation, which can bias subtype-specific estimates. Nonclinical factors such as admission thresholds were not measured. Vaccination status was missing for a substantial share of patients. FluSurv-NET represents about 9 percent of the US population, so results may not fully generalize nationally.1
As of the most recent weekly CDC report for Week 35 ending August 30, 2025, national influenza activity is low. Clinical laboratories reported 0.4 percent positivity, public health laboratories detected only influenza A with A(H1N1)pdm09 predominating, and no new human H5 or H3N2v infections were reported. Outpatient visits for influenza-like illness were 1.8 percent nationally, emergency department visits for influenza were 0.1 percent, hospitals reported 812 laboratory-confirmed admissions at a rate of 0.2 per 100,000, influenza accounted for 0.02 percent of deaths, and one additional pediatric death was reported, bringing the season total to 279. All figures are preliminary.2
CDC continues to recommend annual influenza vaccination for all persons aged 6 months or older without contraindications and timely antiviral treatment for all hospitalized patients with suspected or confirmed influenza to reduce the risk for complications.
References
1.O’Halloran A, Habeck JW, Gilmer M, et al. Influenza-Associated Hospitalizations During a High Severity Season — Influenza Hospitalization Surveillance Network, United States, 2024–25 Influenza Season. MMWR Morb Mortal Wkly Rep 2025;74:529–537. DOI: http://dx.doi.org/10.15585/mmwr.mm7434a1
2.CDC. Weekly US Influenza Surveillance Report: Key Updates for Week 35, ending August 30, 2025. September 5, 2025. Accessed September 12, 2025. https://www.cdc.gov/fluview/surveillance/2025-week-35.html
