Under the Weather: Unpacking the Impact of the 2024-2025 Influenza Season

The 2024-2025 influenza season emerged as one of the most severe in recent history, catching both the public and health care professionals off guard. The past season’s influenza outbreak was classified as high severity—a designation not used in more than 7 years.¹ The US also reported the highest rates of hospitalizations and outpatient visits for flulike illnesses in 15 years.^1,2 As experts explore shifting influenza strains, decreased community immunity, and limited vaccine coverage, lessons from the past season can help strengthen prevention and drive vaccination for 2025-2026.

Image Credit: Feydzhet Shabanov | stock.adobe.com

An Atypical Pattern

In the US, influenza season generally starts in October, peaks from December to February, and gradually tapers off through April or even into May. During the 2024-2025 season, however, influenza cases initially surged above the national baseline in late December, and a second peak emerged in early February.² Hospitalizations mirrored this trend, first reaching just more than 10 per 100,000 people in early January, then climbing to nearly 14 per 100,000 by February’s peak.² From October 2024 to March 2025, the CDC reported at least 37 million influenza infections, 480,000 hospitalizations, and 21,000 deaths.^1,3

Multiple factors combined to make the past influenza season especially severe. The season’s influenza vaccines were less effective than anticipated due to a mismatch between the strains and the dominant circulating viruses, limiting protection for many individuals. According to the CDC, the past influenza season was dominated by 2 influenza A strains: H1N1 (53.7%) and H3N2 (46.3%).^1,3 These strains are known for causing more severe illness and spreading faster than influenza B. H3N2 is especially worrisome because of its frequent mutations, which can hinder immune recognition and response.⁴ Immune response data showed that just 50.9% of H3N2 samples matched well with vaccine antibodies, down from near-total recognition the previous year.⁵

In addition to strain severity and vaccine mismatch, reduced exposure to influenza during the COVID-19 pandemic due to widespread masking, social distancing, and school closures may have left many people with lower immunity in recent years. This immunity gap is particularly concerning among young children, many of whom had limited or no prior exposure to influenza viruses. Those 5 years and younger or with underlying health conditions are especially at risk for serious or even life-threatening complications.⁶ The CDC reported 216 pediatric deaths from influenza during the 2024-2025 season—surpassing the previous nonpandemic season high of 207 deaths in 2023- 2024.⁷ An increase in neurological complications, including seizures, hallucinations, and other concerning symptoms, among children has also been observed.²

Vaccination: still critical but underused.

Getting vaccinated continues to be the most effective way to prevent influenza and its related complications, although overall vaccination rates last season were lower than in recent years, particularly among children and older adults (groups that typically have higher transmission rates). As of March 8, 2025, 147.6 million doses of influenza vaccine were distributed in the US. Influenza vaccination coverage for the 2024-2025 season was stagnant or declined across key populations; as of April 2025, just 49.2% of children, 46.7% of adults, and 38.0% of pregnant women were vaccinated—figures that are slightly lower or nearly unchanged from the prior year. Additionally, vaccination rates among Medicare beneficiaries 65 years and older reached only 48.3%, and nearly 9.2 million fewer doses were administered in retail and clinical settings than in the prepandemic 2019-2020 season.^8,9

Barriers such as systemic inequities, limited health care access, and mistrust in medical institutions—particularly in Black and Hispanic communities continue to prevent many people from getting vaccinated. More than half of White and Asian American adults received an influenza vaccine this past season, compared with just 43% of Black adults and 37% of American Indian, Alaska Native, and Hispanic adults.¹⁰ Others may fear adverse effects or misunderstand the safety and effectiveness of vaccines due to misinformation. Geographic location also affects vaccine access; according to the CDC, only about 40% of adults in rural areas receive influenza vaccinations, compared with 48% of those in urban and suburban areas, and this gap continues to grow.¹¹

Addressing these disparities requires targeted public health strategies, including improving access to health care, providing appropriate education about vaccines, and building trust within communities. Pharmacists can help combat vaccine hesitancy by offering consistent care that addresses misconceptions about vaccine safety. Their presence in rural and underserved areas makes them uniquely positioned to reach individuals who may have limited access to health care services. Talking with patients during every visit creates important opportunities to recommend vaccination and explain how it helps prevent serious illness.

Conclusion

The unprecedented severity of the 2024-2025 influenza season has served as a stark reminder of the virus’ ongoing threat to public health. With record-high pediatric cases, elevated hospitalization rates, and widespread complications, the need for robust prevention has never been more apparent.

References

1. Camero K. Why is the flu so bad this year? NBC News. February 28, 2025. Accessed May 29, 2025. https://www.nbcnews.com/health/health-news/why-flu-bad-2025-severity-vaccines-immunity-rcna194250

2. Lewis T. Why this year’s flu season is the worst in more than a decade. Scientific American. March 6, 2025. Accessed May 29, 2025. https://www.scientificamerican.com/article/why-this-years-fluseason-is-the-worst-in-more-than-a-decade/

3. Al-Hajjar S. The 2024-2025 influenza season: decoding the rise in severe illness and hospitalizations. Int J Ped Adolesc Med.2025;12(1):1-3. doi:10.4103/ijpam.ijpam_51_25

4. Landry J. Why is the flu worse this year? (2025). Respiratory Therapy Zone. Updated March 24, 2025. Accessed May 29, 2025. https://www.respiratorytherapyzone.com/why-is-the-flu-worsethis-year/?utm_source=chatgpt.com

5. Tin A. Flu vaccine this season may be poorly matched, early CDC data suggests. CBS News. February 25, 2025. Accessed May 29, 2025. https://www.cbsnews.com/news/flu-vaccine-match-early-cdcdata-2025/

6. Committee on Infectious Diseases. Recommendations for prevention and control of influenza in children, 2024-2025: policy statement. Pediatrics. 2024;154(4):e2024068507. doi:10.1542/peds.2024-068507

7. Weekly US influenza surveillance report: key updates for week 17, ending April 26, 2025. CDC. May 2, 2025. Accessed May 29, 2025. https://www.cdc.gov/fluview/surveillance/2025-week-17.html

8. Weekly flu vaccination dashboard. CDC. May 7, 2025. Accessed May 29, 2025. https://www.cdc.gov/fluvaxview/dashboard/index.html

9. Influenza vaccine doses distributed. CDC. March 26, 2025. Accessed May 29, 2025. https://www.cdc.gov/fluvaxview/dashboard/vaccine-doses-distributed.html

10. ACIP unanimously recommends updated 2024-2025 COVID-19 and influenza vaccines for most patients. News release. American Pharmacists Association. Accessed May 29, 2025. https://www.pharmacist.com/Blogs/CEO-Blog/acip-unanimouslyrecommendsupdated-2024-2025-covid-19-and-influenza-vaccines-for-mostpatients

11. Disparities in flu vaccination coverage are cause for concern. National Foundation for Infectious Diseases. November 7, 2022. Accessed May 29, 2025. https://www.nfid.org/disparities-in-flu-vaccination-coverage-are-cause-for-concern/