Trivalent seasonal influenza vaccines include two influenza A subtype viruses (H1N1 and H3N2) and one influenza type B virus. Influenza virus strains were selected based on the influenza vaccine production method: egg-based and cell- or recombinant-based.

As a result of the meeting with the federal partners, the FDA recommends that the trivalent formulation of egg-based influenza vaccines for the 2025-2026 U.S. influenza season contain the following:

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

The FDA recommends that the trivalent formulation of cell- or recombinant-based influenza vaccines for the 2025-2026 U.S. influenza season contain the following:

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

Source