Older Adults Drive Hospitalizations, Costs in the US 2024-2025 Influenza Season

The 2024-2025 US influenza season saw high disease severity that led to disproportionate hospitalizations, deaths, and economic burden among older adults, underscoring the need for targeted prevention strategies, according to the Flunomics report published by Sanofi in collaboration with Marco del Riccio, MD, assistant professor at the University of Florence in Italy.1

The 2024-2025 US influenza season hit older adults hardest, driving hospitalizations and costs, while vaccine coverage remained below targets. | Image Credit: Dr_Microbe - stock.adobe.com

Health and Economic Impact of the US 2024-2025 Influenza Season

Following the severe 2024-2025 influenza season, del Riccio and the Sanofi team synthesized data in the Flunomics report to illustrate influenza's wide-ranging impact on individuals, society, and health systems.2 They noted that assessing the true impact of influenza is challenging, as national, regional, and international surveillance systems often leave important gaps.

Earlier this year, the CDC classified the US 2024-2025 influenza season as high severity for all groups, the first such designation since the 2017-2018 season.3 A total of 56 million symptomatic illnesses were recorded from September 29, 2024, to August 30, 2025, with 34% (n = 18.9 million) occurring among adults aged 50 or older.1 Influenza-related deaths were estimated to range from 27,000 to 130,000.

The season also recorded 770,000 influenza-related hospital admissions, with older adults accounting for 77% (n = 590,000) of these admissions. In line with historical trends, the weekly hospitalization rate peaked at 13.5 (range, 1.1-10.2) per 100,000 in early February 2025, the highest weekly rate observed since the 2010-2011 season.

Data from the MarketScan database indicated that the mean cost per influenza-related hospitalization was $29,206 for low-risk adults aged 50 to 64 and $32,231 for high-risk adults in the same age group. Adults aged 18 to 49 incurred a mean hospitalization cost of $25,113 per stay, while those aged 65 and older had slightly lower mean costs at $22,849 per stay.

However, the authors emphasized that the overall system impact of adults aged 65 and older is “far greater” because of their substantially higher hospitalization rates. Adults aged 18 to 49 years were hospitalized at a rate of 6.5 per 100,000, compared with 755.3 per 100,000 among those aged 65 years and older.

“Older adults generate the majority of influenza-related hospital costs not because their individual hospital stays are more expensive, but because they experience vastly higher rates of severe illness requiring hospital care,” they wrote. “As a result, older adults contribute disproportionately to the total economic burden of influenza in the United States…”

Vaccine Guidance, Uptake During the 2024-2025 Season

To improve patient outcomes and mitigate economic impacts, the FDA’s Vaccines and Related Biological Products Advisory Committee recommended a shift from quadrivalent to trivalent influenza vaccines in 2024 due to the continued absence of the B/Yamagata lineage since the COVID-19 pandemic. The CDC’s Advisory Committee on Immunization Practices (ACIP) endorsed this change for the 2024-2025 season, making trivalent vaccines standard in national recommendations.

ACIP also recommended that adults aged 65 years and older receive an age-appropriate vaccine. Although about 93% of influenza vaccines administered to this age group were preferentially recommended formulations, signaling strong recommendation alignment in real-world practice, the overall influenza vaccine coverage rate was 34%.

Specifically, only 25% of adults aged between 50 and 64 years and 58% of those aged 65 years and older received an influenza vaccine; this was lower than the World Health Organization’s target of a 75% vaccination rate.

“Local variability in infrastructure, provider practices, and vaccine availability—particularly in under-resourced regions or facilities—may limit the reach of these recommendations,” the authors wrote. “Without targeted strategies to address these systemic barriers, a significant share of high-risk adults may continue to go unprotected, despite clear national guidance.”

Closing Data Gaps to Better Assess Influenza Impact

They concluded by acknowledging the report’s limitations. Although the US is one of the few countries with published 2024-2025 influenza data, current reporting still does not capture all cases, particularly asymptomatic infections or individuals who did not seek medical care. This likely led to an underestimation of the true burden. Additionally, data on symptomatic cases, hospitalizations, and deaths are based on modeled estimates, not exhaustive counts. Consequently, the authors emphasized the need for further surveillance.

“These limitations highlight the need for improved, real-time data to fully quantify the health and economic burden of influenza in older adults,” they wrote.

References

1. del Riccio M, Sanofi. Flunomics snapshot: United States. Sanofi November 3, 2025. Accessed November 24, 2025. https://www.sanofi.com/assets/dotcom/content-app/articles/your-health/2025/flunomics/country-specific-scorecards/sanofi-flunomics-country-scorecard--us.pdf
2. Flunomics: assessing the true impact of flu. Sanofi. November 3, 2025. Accessed November 24, 2025. https://www.sanofi.com/en/magazine/your-health/flunomics-assessing-the-true-impact-of-flu
3. McCormick B. US flu hospitalizations reach highest levels in over a decade. AJMC®. September 15, 2025. Accessed November 24, 2025. https://www.ajmc.com/view/us-flu-hospitalizations-reach-highest-levels-in-over-a-decade