Early 2025 Influenza Vaccination Trends Following Prior Season and H3N2 Start

As the United States enters the 2025 to 2026 respiratory virus season, early influenza vaccination trends are emerging in the context of last year's high hospitalization rates and moderate vaccine effectiveness. Preliminary CDC data offer the first look at 2025 uptake while reflecting that about one third of hospitalized patients were vaccinated during the 2024 to 2025 season, when both A(H3N2) and A(H1N1)pdm09 circulated widely.¹

This year the CDC has introduced updated recommendations, including universal use of thimerosal-free single-dose formulations and expanded access to FluMist, prompting questions about whether these policy changes may influence vaccination behavior.² NFID and IDSA experts note that clinician communication, simplified vaccine options, and awareness of circulating variants such as the recent H5N5 detection may all shape uptake as the season progresses.

From High-Severity 2024–2025 Season to Early 2025–2026 Trends

CDC FluSurv-NET data characterize the 2024–2025 US influenza season as high severity, with a cumulative hospitalization rate of 127.1 per 100,000, the highest observed since 2010–2011. Across age groups, hospitalization rates were 1.8–2.8 times higher than median historical levels, with the greatest burden among adults ≥75 years (598.8 per 100,000). Underlying medical conditions were present in 89.1% of hospitalized patients, while severity indicators were consistent with prior seasons: 16.8% required ICU care, 6.1% received mechanical ventilation, and 3% died during hospitalization.¹

Investigators attributed the season’s severity to higher incidence rather than changes in virulence and noted key gaps in prevention and treatment: only 32.4% of hospitalized patients had been vaccinated, and antiviral use was lowest among school-aged children (61.6% among 5–17 years). By Week 35 of 2025, national influenza activity had declined to low levels (positivity .4%, ILI 1.8%, hospitalization .2 per 100,000), with A(H1N1)pdm09 predominating and 279 pediatric deaths reported. CDC continued to recommend vaccination for everyone ≥6 months and early antiviral treatment for hospitalized or high-risk patients.¹

Early Data on Vaccine Effectiveness and Uptake in 2024–2025

Interim estimates from four US influenza vaccine-effectiveness networks (IVY, NVSN, US Flu VE, VISION) show that the 2024–2025 trivalent vaccines meaningfully reduced outpatient visits and hospitalizations. Among individuals <18 years, outpatient VE ranged 32%–60%, and hospitalization VE was 63%–78%. Protection was strongest against A(H1N1)pdm09 (outpatient VE up to 72%, hospitalization VE 63%) and more modest but clinically meaningful against A(H3N2) (outpatient VE 42%, hospitalization VE 55%).⁴

Among adults ≥18 years, outpatient VE was 36%–54%, and hospitalization VE 41%–55%.³ Adults 18–64 years had outpatient VE 37–56% and hospitalization VE 48–51%; adults ≥65 years had outpatient VE 18–51% (one estimate non-significant) and hospitalization VE 38–57%.⁴ Vaccination coverage among test-negative controls was generally 20–40% in children and about one third in adults, reflecting continued room to improve uptake. Nearly all sequenced viruses remained well matched to vaccine strains, including clade 2a.3a.1 A(H3N2) and clades 5a.2a and 5a.2a.1 A(H1N1)pdm09.⁴

CDC’s 2025–2026 Recommendations: Trivalent, Thimerosal-Free Single Doses

Against this backdrop, CDC issued its final 2025–2026 guidance on November 17, 2025, reaffirming annual influenza vaccination for all persons ≥6 months and highlighting several changes intended to simplify delivery and reduce barriers. All US vaccines for 2025–2026 are trivalent, targeting A(H1N1)pdm09, A(H3N2), and B/Victoria-lineage viruses.² Egg-based vaccines contain A/Victoria/4897/2022 (H1N1)pdm09-like, A/Croatia/10136RV/2023 (H3N2)-like, and B/Austria/1359417/2021 (B/Victoria)-like strains; cell-based and recombinant vaccines contain A/Wisconsin/67/2022 (H1N1)pdm09-like, A/District of Columbia/27/2023 (H3N2)-like, and the same B/Victoria component.²

CDC now recommends exclusive use of single-dose, thimerosal-free formulations for children, pregnant patients, and adults.² FluMist is newly approved for self- or caregiver administration, and FluBlok’s age indication has expanded to ≥9 years. Manufacturers expect up to 154 million doses this season, with no anticipated supply constraints. Vaccination remains widely available at no cost through insurance coverage, community clinics, HRSA-supported centers, and the Vaccines for Children program.²

Early 2025–2026 Surveillance: H3N2 Dominant but Activity Still Low

CDC’s Week 47 FluView report provides the first detailed snapshot of the new season. Nationally, 5% of respiratory specimens tested by clinical labs were influenza positive, and 2.5% of outpatient visits were for respiratory illness, below the 3.1% baseline but rising.³ CDC estimates 1.1 million illnesses, 11,000 hospitalizations, and 450 deaths so far this season, with no pediatric deaths to date.³ More than 124 million doses of vaccine have been distributed.³

Among 305 subtyped influenza A specimens, 82.3% were A(H3N2) and 17.7% A(H1N1)pdm09; no A(H5) viruses were detected.³ Outpatient ILI and emergency department visits increased primarily among individuals 0–49 years.³ FluSurv-NET documented 905 hospitalizations from October 1 to November 22 (cumulative rate 2.6 per 100,000), with the highest rates in adults ≥65 years (7.5 per 100,000).³

Antigenic analyses of 589 viruses showed strong similarity to vaccine components for A(H1N1)pdm09 and B/Victoria, and partial match for A(H3N2), where 33.3% of viruses were well recognized by antisera to the updated vaccine component.³ Antiviral susceptibility remained highly favorable, with only one A(H1N1)pdm09 virus (0.2%) showing reduced inhibition to oseltamivir and one (0.2%) to baloxavir.³

Implications for Vaccination and Clinical Practice in 2025

Taken together, last season’s high burden, moderate VE, updated recommendations, and early-season trends reinforce a consistent message: vaccination remains the most effective strategy to reduce influenza morbidity and hospitalization, and timely antiviral treatment is essential for high-risk and hospitalized patients.²⁻⁴ Early data suggest persistent gaps in vaccination coverage among both hospitalized populations and test-negative controls, underscoring the importance of routine primary care, pharmacy-based vaccination, and strong clinician recommendations. As H3N2 continues to dominate, clinicians should remain alert to severe respiratory illness, monitor for zoonotic exposures in the context of H5 virus activity, and follow NFID, IDSA, and CDC updates as more data emerge through the core months of the 2025–2026 season.

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. 2025–2026 Flu Season. November 17, 2025. Accessed December 2, 2025. https://www.cdc.gov/flu/season/2025-2026.html

3.CDC. Weekly US Influenza Surveillance Report: Key Updates for Week 47, ending November 22, 2025. December 1, 2025. Accessed December 2, 2025. https://www.cdc.gov/fluview/surveillance/2025-week-47.html

4.Frutos AM, Cleary S, Reeves EL, et al. Interim Estimates of 2024–2025 Seasonal Influenza Vaccine Effectiveness — Four Vaccine Effectiveness Networks, United States, October 2024–February 2025. MMWR Morb Mortal Wkly Rep 2025;74:83–90. DOI: http://dx.doi.org/10.15585/mmwr.mm7406a