US Flu Hospitalizations Reach Highest Levels in Over a Decade

The cumulative influenza-associated hospitalization rate during the 2024-2025 US influenza season was the highest it has been since 2010-2011, according to a study published in the CDC’s Morbidity and Mortality Weekly Report.¹

Earlier this year, the CDC classified the US 2024-2025 influenza season as high severity for all groups, making it the first such season since 2017-2018.² The researchers explained that the CDC determines annual seasonal severity by comparing the current season’s activity with thresholds based on peak activity of past seasons for 3 surveillance indicators, including laboratory-confirmed influenza-associated hospitalization rates from the Influenza Hospitalization Surveillance Network (FluSurv-NET).¹

The 2024-2025 influenza season saw record-high hospitalization rates, prompting the CDC to emphasize the importance of vaccination and early antiviral treatment. | Image Credit: catinsyrup - stock.adobe.com

The researchers used FluSurv-NET data to describe influenza-associated hospitalization rates, clinical characteristics, and outcomes across all age groups, comparing the 2024-2025 influenza season with those of previous years.

FluSurv-NET conducts population-based surveillance of laboratory-confirmed influenza-associated hospitalizations among patients of all ages in about 300 acute care hospitals across 14 states, covering 9% of the US population.³ Preliminary data for the 2024-2025 influenza season were updated on September 2, 2025, with 99% completion for rate estimation and clinical data, as well as 85% completion for vaccination data review.¹

Based on this preliminary data, FluSurv-NET identified 38,960 influenza-associated hospitalizations between October 1, 2024, and April 30, 2025. The overall 2024-2025 cumulative hospitalization rate (127.1 per 100,000) surpassed end-of-season rates from past seasons (median 2010-11 through 2023-24 rate = 62.0 [range, 8.7-102.9]). The researchers noted that the weekly influenza hospitalization rate peaked at 13.5 (range, 1.1-10.2) per 100,000 in early February, which was the highest weekly rate observed since the 2010-2011 season.

Compared with median historical cumulative rates, those during the 2024-2025 season were 1.8 to 2.8 times higher across all age groups. In particular, it was highest in patients aged 75 or older (598.8) and lowest in those between the ages of 5 and 17 (39.3). For patients aged younger than 75, the hospitalization rates were higher during the 2024-2025 season vs past seasons. In contrast, the hospitalization rate for patients aged 75 or older was the second-highest rate after the 2017-2018 season (726.5).

Of 10,269 randomly sampled patients hospitalized with influenza during the 2024-2025 season, the median number of underlying medical conditions ranged from zero to 3 per patient across age groups. The most common underlying conditions were asthma among children aged 0 to 4 (14.0%) and 5 to 17 years (35.9%), obesity among adults aged 18 to 49 years (43.9%), chronic metabolic disease among adults aged 50 to 64 years (45.6%), and cardiovascular disease among adults aged 65 to 74 (57.0%) and 75 years and older (69.3%).

Among patients hospitalized during the 2024-2025 season, 32.4% received an influenza vaccine, and 84.8% received antiviral treatment. Additionally, 16.8% of patients were admitted to an intensive care unit, with 6.1% receiving invasive mechanical ventilation and 3.0% dying in the hospital. Like in past seasons, the most frequent complications during hospitalizations were pneumonia (30.0%), sepsis (18.5%), and acute renal failure (18.1%).

The researchers acknowledged their study’s limitations, including that the FluSurv-NET catchment area represents just 9% of the US population. Because of this, their findings may not be generalizable to the entire US population. Additionally, influenza-associated hospitalizations may be underestimated due to clinician-driven influenza testing. Still, they expressed confidence in their findings and suggested ways to prevent influenza and its subsequent complications.

“All persons aged ≥ 6 months who did not have contraindications are recommended to receive [an] annual influenza vaccination,” the authors concluded. “To reduce the risk of influenza-associated complications, early initiation of antiviral treatment is recommended for all hospitalized patients with suspected or confirmed influenza illness.”

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(34):529-537. doi:10.15585/mmwr.mm7434a1
2. 2024-2025 United States flu season: preliminary in-season severity assessment. CDC. May 23, 2025. Accessed September 15, 2025. https://www.cdc.gov/flu/php/surveillance/in-season-severity.html
3. Naquin A, O’Halloran A, Ujamaa D, et al. Laboratory-confirmed influenza-associated hospitalizations among children and adults—Influenza Hospitalization Surveillance Network, United States, 2010–2023. MMWR Surveill Summ. 2024;73(6):1-18. doi:10.15585/mmwr.ss7706a1