Influenza A(H5N8) vaccine induces humoral and cell-mediated immunity against highly pathogenic avian influenza clade 2.3.4.4b A(H5N1) viruses in at-risk individuals
Finland faced an outbreak of highly pathogenic clade 2.3.4.4b A(H5N1) avian influenza in 2023, which spread from wild birds to fur farms. Vaccinations of at-risk individuals began in June 2024 using the MF59-adjuvanted inactivated A(H5N8) vaccine (Seqirus; A/Astrakhan/3212/2020, clade 2.3.4.4b). Here, in an observational study, we assessed vaccine-induced immune responses in occupational at-risk individuals participating in the phase IV trial, including virus-specific antibody (n = 39 individuals) and T-cell (n = 18 individuals) responses. Vaccination elicited functional antibodies against the vaccine virus and two heterologous clade 2.3.4.4b strains associated with outbreaks on Finnish fur farms and dairy cattle in the United States. Among previously unvaccinated individuals, seroprotection rates against the vaccine virus were 83% (95% CI 70-97%) by microneutralization assay (titre ≥20) and 97% (90-100%) by haemagglutination inhibition assay (titre ≥40). In those previously vaccinated against avian influenza, a single dose induced seroprotection. A(H5N8)-specific memory CD4<sup>+</sup> T-cell responses were detectable, with ~5-fold increase in IFNγ secretion after two doses. These results demonstrate that the vaccine probably provides cross-protection against circulating H5 clade 2.3.4.4b viruses. EU Clinical Trial Number 2023-509178-44-00.
Authors
- Alessandro Sette (ORCID: https://orcid.org/0000-0001-7013-2250)
- Maija Lappalainen (ORCID: https://orcid.org/0000-0001-5400-1250)
- Ritva Syrjänen (ORCID: https://orcid.org/0000-0002-1077-6617)
- Arttu Reinholm (ORCID: https://orcid.org/0000-0001-5142-1612)
- Saimi Vara
- Riikka Holopainen (ORCID: https://orcid.org/0009-0003-2122-8741)
- Merit Melin (ORCID: https://orcid.org/0000-0001-9375-4327)
- Theo M. Bestebroer
- Rory D. de Vries (ORCID: https://orcid.org/0000-0003-2817-0127)
- Anu Haveri (ORCID: https://orcid.org/0000-0003-4620-7536)
- Willemijn F. Rijnink (ORCID: https://orcid.org/0000-0003-3151-3725)
- Erika Lindh (ORCID: https://orcid.org/0000-0002-9168-1053)
- Oona Liedes (ORCID: https://orcid.org/0009-0007-1570-4325)
- Niina Ikonen (ORCID: https://orcid.org/0000-0003-0724-8888)
- Ilkka Julkunen
- Mathilde Richard (ORCID: https://orcid.org/0000-0003-0240-9312)
- Nina Ekström (ORCID: https://orcid.org/0000-0003-2220-9027)
- Terhi Laaksonen
- Pinja Jalkanen (ORCID: https://orcid.org/0000-0001-7218-4732)
- Laura Kakkola (ORCID: https://orcid.org/0000-0001-9271-4059)
- Pekka Kolehmainen (ORCID: https://orcid.org/0000-0001-5997-8167)
- Alba Grifoni
- Anna Solastie
- Hanna Nohynek
Institutions
- La Jolla Institute for Immunology (US)
- University of Turku (FI)
- Helsinki University Hospital (FI)
- Erasmus MC (NL)
- Turku University Hospital (FI)
- University of California San Diego (US)
- Finnish Institute for Health and Welfare (FI)
- Finnish Food Authority (FI)
Publication Details
- Journal
- Nature Microbiology
- Published
- 2025-12-05
- DOI
- https://doi.org/10.1038/s41564-025-02183-5
- Citations
- 2
- Primary Topic
- Influenza Virus Research Studies
- Type
- article
- Field-Weighted Citation Impact
- 2.71
Funders
- Helsingin Yliopisto
- European Commission
- ZonMw
- Turun Yliopisto
- Biocenter Finland