How Did Last Year’s Vaccines Fare?

Updated 2025-26 flu and COVID-19 vaccines both provide meaningful, if moderate, protection against hospitalization and medically attended illness, based on interim real-world effectiveness data released during the current season. Flu vaccine effectiveness (VE) is lower this year than in recent seasons because of antigenic drift from the emergent A(H3N2) subclade K, but vaccination still reduces illness and hospitalization. COVID-19 vaccines updated to the LP.8.1 strain show roughly 50-55% protection against medically attended COVID-19 and hospitalization.

2025-26 influenza vaccine effectiveness

• U.S. interim CDC estimates (MMWR, three VE networks): Among children/adolescents <18 years, VE was 38-41% against outpatient influenza and 41% against influenza-associated hospitalization. Among adults ≥18 years, VE was 22-34% against outpatient visits and 30% against hospitalization. VE against influenza B was higher (45-71% in children, 63% in adults). [1]
• California interim data: Overall VE was 33% against any influenza (39% in children, 22% in adults ≥65), 32% against influenza A, and 47% against influenza B. [2]
• Adults 18-64 (VISION/Flu VE registries): VE of 29% against hospitalization and 24-36% against lab-confirmed infection. [3]
• Canada (sentinel network): ~40% reduction in medically attended illness from predominant A(H3N2), including subclade K, and ~30% against A(H1N1)pdm09. [4]

The CDC and ACIP attribute the reduced VE this season to the drifted A(H3N2) subclade K (J.2.4.1), which emerged after strain selection and now accounts for >90% of subtyped H3N2 viruses. [5-6] Despite this mismatch, data from the UK, Canada, and the U.S. indicate meaningful residual protection against severe disease, and annual vaccination remains recommended for all persons ≥6 months. [1][5-6]

2025-26 COVID-19 vaccine effectiveness

• U.S. interim CDC estimates (test-negative design, Sep-Dec 2025): In immunocompetent adults ≥18 years, the 2025-2026 vaccine was 50% effective against COVID-19-associated ED/urgent care encounters and 55% against hospitalization, representing protection beyond existing immunity. [7]
• LP.8.1-adapted BNT162b2 (real-world): Demonstrated early effectiveness against ED/UC and outpatient visits during the 2025-26 season. [8]
• 2026-27 JAMA systematic review (incorporating 2025-26 data): Updated vaccines reduced hospitalization risk in adults ≥65 (VE 53%) and in adults 18-64 (VE 54%, 2024-25 season); maternal vaccination protected infants (VE 50-54%); and immunocompromised adults had reduced critical illness (VE 32-53%). [9]
• NEJM evidence synthesis for 2025-26: Pooled VE against hospitalization for XBB.1.5-adapted mRNA vaccines was 46-50% in adults and 37% in immunocompromised adults, with no new safety signals. [10]

The 2025-26 formulations (Comirnaty, Spikevax/mNEXSPIKE, Nuvaxovid) target the JN.1-lineage LP.8.1 strain and generate strong neutralizing antibody responses; immunogenicity trials showed ~4-fold titer increases two weeks post-vaccination. [11-12] Safety profiles are consistent with prior formulations. [9-11]

The following figure from a U.S. Veterans study illustrates the sustained, cumulative protection of updated COVID-19 vaccination against ED visits, hospitalization, and death over 180 days (2024-2025 season data):

Figure 2. Cumulative Risks of Covid-19–Associated Outcomes over 180 Days in the 2024–2025 Vaccination Season.

Association of 2024–2025 Covid-19 Vaccine with Covid-19 Outcomes in U.S. Veterans. N Engl J Med. October 23, 2025.

Used under license from The New England Journal of Medicine.

Practical takeaways

• Both vaccines may be coadministered safely with similar immunogenicity to sequential dosing. [10][14]
• Flu VE is lower but still protective this season; protection against influenza B and against severe outcomes remains substantial. [1][5]
• COVID-19 vaccination offers additional protection beyond prior immunity, with the greatest absolute benefit in older and high-risk adults. [7][9]