{
  "abstract": "BackgroundThe 2025/26 influenza season included A(H3N2) subclade K predominance with A(H1N1)pdm09 co-circulation and subsequent prolonged influenza B activity. The Canadian Sentinel Practitioner Surveillance Network reports vaccine effectiveness (VE) in the context of genetic and antigenic relatedness to circulating viruses.\n\nMethodsWe estimated VE by test-negative design among outpatients with medically-attended acute respiratory illness between November and April. We characterized case viruses by whole genome sequencing and hemagglutination inhibition assay.\n\nResultsAmong 2809/9047 (31%) influenza-positive specimens, 82% (2306/2809) were influenza A with 18% (504/2809) influenza B. Of subtyped influenza A, 85% (1848/2169) were A(H3N2).\n\nWe sequenced 59% (1099/1848) of A(H3N2) viruses, with 87% (956/1099) subclade K, antigenically-mismatched to subclade J.2 vaccine. VE against A(H3N2) and subclade K was 38% (95% confidence interval: 27%-47%) and 33% (19%-45%).\n\nWe sequenced 69% (222/323) of A(H1N1)pdm09 viruses, virtually all (n=218) clade 5a.2a.1, including subclades D.3.1 (21%; n=47) and D.3.1.1 (77%; n=171), antigenically-matched to subclade D vaccine. VE against A(H1N1)pdm09, subclades D.3.1 and D.3.1.1 was 28% (4%-47%), -21% (-144%-40%) and 44% (14%-64%).\n\nWe sequenced 82% (413/504) of influenza B viruses, all B/Victoria, including antigenically-mismatched subclade C.3 (18%; n=74) with D197N gain-of-glycosylation, and antigenically-matched subclade C.5 (82%; n=339) relative to subclade C vaccine. VE against influenza B, subclades C.3 and C.5 was 55% (41%-66%), 10% (-60%-49%) and 68% (51%-79%).\n\nConclusionsThe 2025/26 influenza vaccine reduced the risk of A(H3N2), A(H1N1)pdm09 and B/Victoria by over one-third, one-quarter and one-half, respectively. Laboratory-based indicators of vaccine match remain uncertain proxies for actual vaccine protection, reinforcing importance of annual epidemiological monitoring of VE.",
  "abstract_shown": true,
  "affiliations": [
    "British Columbia Centre for Disease Control"
  ],
  "article_type": "PUBLISHAHEADOFPRINT",
  "arxiv": null,
  "author_total": 20,
  "authors": [
    {
      "name": "L. Separovic"
    },
    {
      "name": "S. E. Kaweski"
    },
    {
      "name": "M. B. Cox"
    },
    {
      "name": "Y. Zhan"
    },
    {
      "name": "S. Sabaiduc"
    },
    {
      "name": "R. Olsha"
    },
    {
      "name": "M. Hasso"
    },
    {
      "name": "R. G. Mather"
    },
    {
      "name": "S. Carazo"
    },
    {
      "name": "C. Lacroix"
    },
    {
      "name": "I. Meunier"
    },
    {
      "name": "L. N. Salhi"
    },
    {
      "name": "J. A. Dickinson"
    },
    {
      "name": "N. Zelyas"
    },
    {
      "name": "A. N. Jassem"
    },
    {
      "name": "K. Dover"
    },
    {
      "name": "C. Ranadheera"
    },
    {
      "name": "R. Gao"
    },
    {
      "name": "N. Bastien"
    },
    {
      "affs": [
        0
      ],
      "name": "D. M. Skowronski"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/aat9nkvq26zwg.bib",
  "cited_by": 0,
  "doi": "10.64898/2026.09.10.26362769",
  "fulltext_url": "https://www.medrxiv.org/content/10.64898/2026.09.10.26362769v1.full",
  "id": "aat9nkvq26zwg",
  "issns": [],
  "landing_url": "https://www.medrxiv.org/content/10.64898/2026.09.10.26362769v1",
  "language": null,
  "licence": "CC-BY-NC-ND",
  "licence_label": "CC BY-NC-ND",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by-nc-nd/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "medrxiv",
      "public and global health"
    ],
    [
      "openalex",
      "2713|Influenza Virus Research Studies"
    ]
  ],
  "openalex": "W7212389232",
  "pdf_url": "https://www.medrxiv.org/content/10.64898/2026.09.10.26362769v1.full.pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-10",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/aat9nkvq26zwg.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:18:27Z",
      "native_id": "10.64898/2026.09.10.26362769",
      "source": "medrxiv",
      "url": "https://www.medrxiv.org/content/10.64898/2026.09.10.26362769v1"
    }
  ],
  "subjects": [
    {
      "field": "medicine",
      "origin": "medrxiv:public and global health",
      "subfield": "epidemiology-public-health"
    }
  ],
  "title": "2025/26 subclade-specific influenza A and B vaccine effectiveness estimates and discordant laboratory-based indicators of vaccine match or mismatch",
  "title_text": "2025/26 subclade-specific influenza A and B vaccine effectiveness estimates and discordant laboratory-based indicators of vaccine match or mismatch",
  "type": "preprint",
  "updated_at": "2026-10-30T12:18:27Z",
  "url": "https://research.draconitic.com/paper/aat9nkvq26zwg",
  "venue": "medRxiv",
  "versions": []
}