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What H3N2 variants are predicted for the 2025-2026 flu season?
Executive Summary
Public health authorities have selected two different A(H3N2) candidate vaccine viruses for the 2025–2026 Northern Hemisphere influenza vaccine: A/Croatia/10136RV/2023‑like for egg‑based vaccines and A/District of Columbia/27/2023‑like for cell‑ or recombinant‑based vaccines. These selections reflect laboratory antigenic data, prior season circulation dominated in part by H3N2, and ongoing concerns about egg‑adaptation altering antigenicity.
1. Why two H3N2 picks — and what that signals about risk this winter
Regulators split the H3N2 recommendation by production platform because egg‑propagation can introduce mutations that change antigenic sites, potentially reducing match to circulating viruses; cell‑ and recombinant‑based vaccines avoid most egg‑adaptation effects. The U.S. CDC published the vaccine composition for 2025–2026 listing A/Croatia/10136RV/2023‑like for egg vaccines and A/District of Columbia/27/2023‑like for cell/recombinant vaccines, reflecting the FDA and WHO technical advice and laboratory serology showing those candidates best represent recent circulating A(H3N2) diversity [1] [2] [3]. This dual choice is a pragmatic response to production realities and the persistent dominance of H3N2 in recent seasons; it does not guarantee perfect match but reduces the chance of broad vaccine escape.
2. What the Southern Hemisphere and recent surveillance suggest about likely H3N2 circulation
Surveillance from the 2024–2025 season and Southern Hemisphere patterns informed the vaccine strain decision because southern circulation often foreshadows northern trends. Public analyses show A(H3N2) accounted for a large share of subtyped influenza A viruses in 2024–2025, and Southern Hemisphere reports highlighted ongoing H3N2 activity alongside H1N1pdm09 and B/Victoria lineages [4] [5]. WHO and regulatory committees synthesize antigenic, genetic, and epidemiologic data; the 2025 selections therefore represent a best‑fit prediction against observed antigenic clusters rather than a definitive forecast of which subvariants will dominate every region [3] [5]. Regional differences and viral evolution can still shift dominance mid‑season.
3. How experts judged antigenic match and vaccine performance expectations
Committee statements and vaccine composition notices emphasize laboratory serology showing the chosen candidate viruses recognize the majority of currently circulating A(H3N2) strains, which is the primary criterion for selection [6] [3]. However, real‑world vaccine effectiveness historically varies greatly for H3N2 because this subtype evolves rapidly and because egg‑adaptation can reduce efficacy of egg‑based vaccines. By recommending different candidates by platform, authorities aim to preserve the best possible match for each manufacturing pathway, hoping to improve population‑level protection compared with a one‑size‑fits‑all choice [2] [6]. This approach trades manufacturing complexity for potentially better antigenic fidelity.
4. Divergent views and potential agendas behind the messaging
Public health agencies frame the dual‑strain decision as science‑driven and precautionary; vaccine manufacturers emphasize the need for lead time and supply stability. Some advocacy groups and commentators push for faster uptake of cell‑based and recombinant platforms, arguing egg adaptation repeatedly undermines H3N2 protection, while legacy manufacturers underscore existing egg capacity to meet demand quickly [2] [1]. These positions reflect competing operational and commercial interests: improving antigenic match versus ensuring nationwide vaccine availability. Readers should note messaging from industry and advocacy sources may emphasize different metrics—antigenic fidelity or throughput—when interpreting the same technical recommendation.
5. Alternatives, uncertainties, and how to interpret “predicted variants”
The phrase “predicted H3N2 variants” should be read as a technical selection of candidate vaccine viruses rather than a firm forecast of circulating lineages. WHO’s Northern Hemisphere recommendation names A/Croatia/10136RV/2023‑like and A/District of Columbia/27/2023‑like as the composition for 2025–2026, but mid‑season antigenic drift or regionally dominant subclades could reduce match [3] [2]. The WHO’s later Southern Hemisphere recommendations for 2026 list different H3N2 candidates, illustrating how rapidly the target can shift [7]. Public health guidance therefore couples strain selection with surveillance and clinical outcome monitoring to update recommendations and risk communications through the season.
6. Bottom line for clinicians, policymakers, and the public this season
For 2025–2026 the actionable fact is clear: vaccine formulations will include A/Croatia/10136RV/2023‑like for egg‑based products and A/District of Columbia/27/2023‑like for cell/recombinant products, reflecting the best available antigenic fit at the time of selection [1] [2] [3]. Stakeholders should expect variable effectiveness against H3N2 depending on vaccine platform and viral evolution; ongoing global surveillance data will determine whether substantial drift occurs during the season [4]. Widespread vaccination remains the primary public‑health tool to reduce severe outcomes even when subtype match is imperfect.