Which influenza A and B strains are included in the 2025–2026 Northern Hemisphere flu vaccine?

1. What exactly is in the 2025–2026 U.S. flu vaccine — the named strains

For the U.S. 2025–2026 season, the FDA’s recommendations for egg-based vaccines list 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 informed manufacturers of these candidate vaccine strains after its interagency review ^[2]. The CDC also states that all U.S. flu vaccines for 2025–2026 are anticipated to be trivalent and will protect against an A(H1N1), an A(H3N2) and a B/Victoria virus ^[1].

2. Why trivalent this year — the shift away from quadrivalent

Both U.S. and EU guidance for 2025–2026 emphasize trivalent vaccines (two A strains + one B), reflecting the decision to omit B/Yamagata from routine formulations because that lineage has not been seen consistently in recent surveillance; the European Medicines Agency noted a planned transition from quadrivalent to trivalent vaccines that do not include B/Yamagata for 2025/2026 ^[3]. U.S. agencies likewise indicate that all licensed vaccines will be trivalent for this season ^{[1] [4]}.

3. Different production methods — egg-based vs cell/recombinant nuance

The FDA’s strain recommendations distinguish vaccine production methods: egg-based and cell- or recombinant-based vaccines can have slightly different candidate viruses or updates due to how strains adapt during manufacturing. Reporting notes that strains were selected based on the production method and that the included strains reflect those differences ^{[5] [6]}. Vaccine-makers such as Sanofi confirmed they adopted the FDA-selected strains for their product lines ^[7].

4. What changed from 2024–2025 — the important updates

Most sources say only modest changes from the prior season. Vaccine-advice coverage highlighted that the primary update was an H3N2 strain change (and some reporting flagged A/H2N2 wording in one article, which appears to be a reporting error) while keeping a trivalent formulation; authoritative coverage from Vaccine Advisor and FDA details the specific A(H1N1), A(H3N2) and B/Victoria selections ^{[8] [2]}. Pharmacy Times suggested an “A/H2N2” mention, but that conflicts with FDA/CDC reporting listing H1N1 and H3N2 as the two A subtypes ^{[8] [1] [2]}. Available sources do not mention inclusion of any H2N2 seasonal strain in official recommendations (not found in current reporting).

5. Who decided — process and players

The FDA made the formal U.S. recommendations after consulting with federal partners (CDC, Department of Defense) and reviewing surveillance data; an interagency panel informed manufacturers on March 13, 2025 ^{[2] [5]}. The WHO issues separate northern-hemisphere recommendations globally; WHO documentation on the 2025–2026 Northern Hemisphere composition is listed among the reference materials but the primary U.S. decisions and the specific strain names cited here come from the FDA/CDC materials ^{[9] [1]}.

6. Limitations, disagreements and reporting caveats

Reporting differences exist: some secondary articles mis-stated or mis-typed strain subtypes (for example, Pharmacy Times referenced A/H2N2 in context of updates, which conflicts with primary FDA/CDC listings showing H1N1 and H3N2 as the A subtypes) — the FDA, CDC and Vaccine Advisor materials consistently identify H1N1, H3N2 and B/Victoria strains ^{[8] [2] [1]}. Surveillance uncertainty always matters: as NPR noted, strain selection is a forecast based on global surveillance and laboratory analysis, and reduced international surveillance participation could affect future strain tracking ^[10]. WHO materials and EU guidance also note continuous virus evolution and that recommendations are periodically adjusted ^{[9] [3]}.

7. Practical takeaways for clinicians and the public

Clinicians and immunizers should expect trivalent vaccines in U.S. supplies for 2025–2026 and that manufacturers (Sanofi and others) plan to ship products consistent with FDA recommendations — everyone should check product labeling for the exact candidate-virus names for a given vaccine lot ^{[7] [2]}. Public-health context: the vaccine targets the main circulating A and B/Victoria lineages for the season; surveillance-driven mismatches remain possible and agencies stress annual vaccination as the best available protection ^{[1] [2]}.