Updates on influenza vaccine strain recommended by WHO (2025-2026 northern hemisphere)

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

Table 1. Key updates of influenza vaccine composition for the 2025–2026 northern hemisphere influenza season.

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) substituted with 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

Table 2. Key target antigens (HA, NA, NP) play vital roles in influenza vaccine, drug, and diagnostic development.

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.

Figure 1. Recombinant HA protein used to measure serum antibody levels in vaccinated mice ² Image Credit: Sino Biological Inc.

IV. Sino Biological unveils comprehensive influenza research reagents for 2025-2026 vaccine strains

Sino Biological, a leading provider of biological reagents and services, has announced the release of its latest portfolio of influenza research reagents. Designed to support the development of vaccines for the 2025-2026 northern hemisphere influenza season, the new offerings include high-quality recombinant HA, NA, and NP proteins. These reagents are now available for immediate prder, providing researchers with the tools they need to accelerate their studies and contribute to global influenza prevention efforts.

References:

1. WHO (2025). Recommendations announced for influenza vaccine composition for the 2025–2026 northern hemisphere influenza season. (online) WHO. Available at: https://www.who.int/news/item/28-02-2025-recommendations-announced-for-influenza-vaccine-composition-for-the-2025-2026-northern-hemisphere-influenza-season.
2. Andersen, T.K., et al. (2021). Pandemic Preparedness Against Influenza: DNA Vaccine for Rapid Relief. Frontiers in Immunology, 12. https://doi.org/10.3389/fimmu.2021.747032.