CDC: Last Flu Season Produced Highest Hospitalization Rate in Over a Decade

Federal health officials say hospitalizations linked to influenza surged to levels not seen in more than a decade during the 2024–25 season, with nearly 39,000 people admitted for laboratory-confirmed flu between October and April.

The Centers for Disease Control and Prevention reported a cumulative hospitalization rate of 127.1 per 100,000 people in FluSurv-NET, more than double the 14-season average of 62 per 100,000 and the highest season on record since the system began reporting comparable data in 2010. Hospital admissions peaked in early February at the highest weekly rate recorded in the past decade.

The CDC’s FluSurv-NET surveillance system draws from roughly 300 hospitals across 14 states, representing an estimated nine percent of the U.S. population—about 31 million people. The system tracks laboratory-confirmed influenza cases severe enough to require hospitalization and, for a selected subset, extracts detailed clinical information from medical records to determine vaccination status, underlying conditions and intensive-care needs.

Unvaccinated people accounted for the overwhelming majority of hospitalizations, making up more than 70 percent of admissions, the agency said. Clinical outcomes for hospitalized patients were consistent with those seen in previous severe seasons: 17 percent required intensive care unit treatment, 6 percent were placed on mechanical ventilation and 3 percent died during their hospital stay. The CDC did not provide a single, aggregate death tally for the season.

Complications were common. Pneumonia developed in about 30 percent of hospitalized patients, sepsis in roughly 18.5 percent, and acute kidney failure in about 18 percent. Influenza A viruses drove the season’s severity; H1N1 circulated most widely overall and produced higher hospitalization rates among older adults than the H3N2 strain, a reversal from the 2017–18 season when H3N2 posed the greatest risk for seniors.

Risk factors varied by age. For children, asthma was the most common underlying condition, affecting 14 percent of hospitalized infants and toddlers up to age 4 and nearly 40 percent of school-aged children and adolescents ages 5 to 17. The American Academy of Pediatrics estimated 216 pediatric deaths during the season, making it the deadliest non-pandemic flu season on record for U.S. children, although the CDC did not provide a single, consolidated pediatric death count in its report. Among adults 18 to 49, obesity was present in about 44 percent of hospitalized patients. Chronic metabolic disease, primarily diabetes, affected 45.6 percent of patients aged 50 to 64. Cardiovascular disease was the predominant risk factor for older adults, present in 57 percent of those 65 to 74 and 69 percent of patients 75 and older.

The CDC noted treatment patterns showed most hospitalized patients—about 85 percent—received antiviral medication such as oseltamivir (Tamiflu), which can reduce the severity and duration of influenza illness. Treatment rates were lowest among children and adolescents, a disparity the report attributed in part to parental perceptions that healthy children may not need antiviral therapy.

Vaccine protection and policy remain central to federal prevention efforts. The World Health Organization and CDC-affiliated scientists convene annually to select strains for the upcoming season’s vaccine. The 2025–26 U.S. vaccine is trivalent, designed to protect against an influenza A(H1N1)-like virus, an influenza A(H3N2)-like virus and a B/Victoria lineage-like virus.

Last season’s vaccine was estimated by the CDC to be 41 percent to 78 percent effective at preventing flu-related hospitalizations and 32 percent to 60 percent effective at preventing less severe infections that still required a medical visit. Health officials emphasize that effectiveness depends on how well the selected vaccine strains match circulating viruses and that protection declines over time, making October the optimal month for vaccination in most years.

The CDC continues to recommend annual influenza vaccination for everyone 6 months of age and older, including healthy young people and those without chronic conditions. Flu shots are typically covered at no cost by most insurers under recommendations from the CDC; out-of-pocket prices for uninsured individuals vary by pharmacy and can range from about $20 to $120. Public health clinics frequently offer free vaccination events.

Influenza causes a wide spectrum of illness, from mild respiratory symptoms to life-threatening complications. Federal estimates place average annual U.S. influenza deaths at about 36,000, with the highest risks for older adults—particularly those 75 and older—and for people with respiratory disease, obesity, heart disease and other chronic conditions.

With the 2025–26 season approaching, the CDC urged vaccination in the fall, early antiviral treatment for those at higher risk or with severe illness, and continued surveillance of circulating strains. The agency’s report underscores the variability of seasonal influenza and the role of vaccination and early treatment in reducing severe outcomes and hospital strain.