I. Updates on 2025-2026 Northern Hemisphere Influenza Vaccine Strains

To maintain vaccine efficacy, WHO regularly updates influenza vaccine strains based on global epidemiological, virological, and serological analyses. On February 28, 2025, WHO announced the recommended strains for the 2025-2026 northern hemisphere influenza season1:

1. Trivalent egg-based vaccines

an A/Victoria/4897/2022 (H1N1)pdm09-like virus
an A/Croatia/10136RV/2023 (H3N2)-like virus
a B/Austria/1359417/2021 (B/Victoria lineage)-like virus

2. Trivalent cell culture- or recombinant protein-based vaccines

an A/Wisconsin/67/2022 (H1N1)pdm09-like virus
an A/District of Columbia/27/2023 (H3N2)-like virus
a B/Austria/1359417/2021 (B/Victoria lineage)-like virus

3. Quadrivalent egg- or cell culture/recombinant-based vaccines (unchanged from 2024)

a B/Phuket/3073/2013 (B/Yamagata lineage)-like virus
 

II. Comparison of 2024-2025 vs. 2025-2026 Vaccine Components

1. H3N2 Strain Substitution
Egg-based vaccines: 2022 strain (A/Thailand/8/2022) substituted with A/Croatia/10136RV/2023 (H3N2).
Cell/recombinant vaccines: 2022 strain (A/Massachusetts/18/2022) substitutedwith A/District of Columbia/27/2023 (H3N2).

2. No Changes to H1N1 or B/Victoria Lineage
H1N1 strains (egg: A/Victoria/4897/2022; cell/recombinant: A/Wisconsin/67/2022) and B/Victoria lineage (B/Austria/1359417/2021) remain unchanged.

3. Summary
Core change: Updated H3N2 strains reflect their high mutation rate.
Continuous development: Consecutive adjustments to H3N2 highlight the need for rapid vaccine adaptation to viral evolution.

III. Recombinant Antigens: Critical Materials for Vaccine Research

Applications of Recombinant Antigens:

Vaccine development: Used in potency testing, ELISA-based antibody level analysis, and quality control.
Research acceleration: Replace traditional viral culture methods, shortening R&D timelines.