What were the overall vaccine effectiveness estimates for 2025–2026 influenza vaccines against A/H1N1, A/H3N2, B/Victoria, and B/Yamagata?
Executive summary
Available public reporting for the 2025–2026 influenza vaccines confirms that formal effectiveness analyses exist (notably interim Southern Hemisphere and early European primary-care studies) but the documents provided here do not contain clear, extractable overall percentage vaccine effectiveness estimates by subtype (A/H1N1, A/H3N2, B/Victoria, B/Yamagata), so precise numeric VE figures cannot be reported from these sources alone [1] [2].
1. What the surveillance reports actually contain: studies and scope
Multi-country primary-care test-negative studies in Europe included 866 influenza cases and 4,165 test-negative controls between weeks 41–49, 2025, and found almost all cases were influenza A (865/866), meaning early European data cannot produce robust B-lineage VE estimates because B cases were essentially absent [2]. Separately, interim effectiveness reports from eight Southern Hemisphere countries analyzed vaccine performance during their 2025 season and were explicitly cited as informative for anticipating Northern Hemisphere protection because the 2025–2026 Northern Hemisphere vaccine composition matched the Southern formulation [1] [3].
2. Why numeric VE numbers are not extractable from the provided reporting
The supplied snippets and documents identify study scopes, vaccine strain compositions, and broad characterizations (for example, “moderate” protection in some reporting), but they do not include the specific point estimates or confidence intervals for VE against each subtype in the material provided to this briefing; therefore asserting exact percentages would go beyond what these sources allow [1] [2] [4].
3. Signals about subtype-specific performance that do appear in the record
There is consistent evidence across sources that A(H3N2) dominated early 2025–2026 season circulation in multiple settings (England and the U.S. commentary), and laboratory antigenic data showed reduced reactivity of vaccine-type antisera against newly circulating H3N2 subclade K viruses—a laboratory correlate consistent with lowered VE against some H3N2 variants [5] [4]. By contrast, the European primary-care early-season sentinel data were overwhelmingly A(H1N1) or other A types in the small window sampled, limiting conclusions about B/Victoria VE there [2].
4. What the vaccine composition and product mix mean for B/Yamagata estimates
For 2025–2026, public authorities recommended trivalent vaccines in many jurisdictions that include A(H1N1), A(H3N2), and B/Victoria components, while B/Yamagata components appear only in quadrivalent formulations or in specific recommendations for Southern Hemisphere or prior seasons described by WHO/GISAID materials; that vaccine-product mix constrains population-level VE against B/Yamagata in places using trivalent-only programs because many recipients were not offered a Yamagata antigen [6] [7] [8].
5. Interpretation, uncertainty, and the practical takeaways
Taken together, the reporting implies that clinicians and public health authorities anticipated moderate protection from the 2025–2026 vaccines overall and urged vaccination while monitoring for H3N2 immune-escape signals [1] [4]; however, because the provided sources here do not include the numerical VE estimates by subtype (A/H1N1, A/H3N2, B/Victoria, B/Yamagata), a definitive numeric answer cannot be produced from this dataset alone and readers should consult the full MMWR/PMC reports and national VE updates for the specific point estimates and confidence intervals referenced in those analyses [1] [3] [5].