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A Retrospective Cross-Sectional Study (2009-2023): Exploring Influenza A(H1N1)pdm09 Antibody Time Series in Humans and Swine and Vaccine Coverage in Two Target Groups.

Solveig Jore¹ Ragnhild Tønnessen² Carl Andreas Grøntvedt² Kjersti Rydland³ Anna Germundsson Hauge² Olav Hungnes⁴ Anja Bråthen Kristoffersen⁵ Even Fossum⁴

Affiliations 5 institutions

Section of Zoonotic & Waterborne Infections, Department of Infection Control and Preparedness, Norwegian Institute of Public Health, Oslo, Norway.
Norwegian Veterinary Institute, Ås, Norway.
Section of Respiratory, Bloodborne and Sexually Transmitted Infections, Department of Infection Control and Vaccine, Norwegian Institute of Public Health, Oslo, Norway.
Department of Virology, Norwegian Institute of Public Health, Oslo, Norway.
Department of Method Development and Analytics, Norwegian Institute of Public Health, Oslo, Norway.

PMID 41857313 2026 Zoonoses Public Health eng ppublish

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Publication summary

Swine may act as 'epidemiological bridges' and reservoirs for the emergence of novel zoonotic influenza viruses with pandemic potential. While bidirectional exchange of influenza A viruses at the swine-human interface is well recognised, data on the extent of interspecies transmission are limited. We analysed the post-seasonal geometric mean titre (GMT) of influenza A(H1N1)pdm09 antibodies in humans and the seasonal prevalence of influenza A(H1N1)pdm09 antibodies in unvaccinated swine from 2009/2010-2022/2023 per county in Norway to search for evidence of interspecies transmission. We explored correlations at the national and individual county level and investigated possible associations by running a negative binomial regression model. Additionally, we distributed an influenza vaccination questionnaire to veterinarians and farmers working with swine to assess vaccination uptake and calculated total response rates per county and overall. The time series of H1N1pdm09 antibodies from humans and swine show significant positive correlations both across (0.8 Pearson correlation coefficient) and within certain individual counties, with especially high correlations in Innlandet (0.9), Vestland (0.8) and Rogaland (0.7) Counties. Our regression analysis revealed a significant positive association between the annual GMT of H1N1pdm09 antibodies in humans, the annual seroprevalence of H1N1pdm09 antibodies in swine, and the density of swine farms in counties. Vaccination uptake was 39% and 50% in farmers and veterinarians, respectively. Our findings indicate a temporal relationship between the disease in humans and swine; suggesting spillover, environmental factors facilitating disease spread, and/or indirect relationships driven by unknown factors. The time series of H1N1pdm09 antibodies in humans and swine shows significant correlations. Regression analysis links GMT of H1N1pdm09 antibodies in humans to seroprevalence of H1N1pdm09 in swine and density of swine farms. This indicates a temporal relationship possibly due to spillover, shared risk factors or indirect relationships driven by unknown factors. The influenza vaccination survey showed a 39% uptake among farmers and 50% among swine veterinarians.

geometric mean titre H1N1pdm09 Norway seroprevalence swine influenza vaccine coverage Antibodies, Viral Influenza A Virus, H1N1 Subtype Influenza Vaccines Influenza, Human Orthomyxoviridae Infections Swine Diseases Animals Cross-Sectional Studies Humans Norway Retrospective Studies Seroepidemiologic Studies

Structured evidence records

Evidence records

2 total

Serological Evidence 2 records

Serological Evidence Extraction confidence 1.00

Key finding

Influenza A(H1N1)pdm09 antibodies were detected in both humans and unvaccinated swine in Norway, with a significant correlation between human GMT and swine seroprevalence indicating possible interspecies transmission or shared exposure.

Virus

Host

Location

Supporting text

We analysed the post-seasonal geometric mean titre (GMT) of influenza A(H1N1)pdm09 antibodies in humans and the seasonal prevalence of influenza A(H1N1)pdm09 antibodies in unvaccinated swine from 2009/2010-2022/2023 per county in Norway to search for evidence of interspecies transmission. The time series of H1N1pdm09 antibodies from humans and swine show significant positive correlations.

Sample type: blood; serum

Serological Evidence Extraction confidence 1.00

Key finding

Humans in Norway showed measurable post-seasonal GMT levels of influenza A(H1N1)pdm09 antibodies from 2009 to 2023, correlated with antibody prevalence in swine.

Virus

Host

Location

Supporting text

We analysed the post-seasonal geometric mean titre (GMT) of influenza A(H1N1)pdm09 antibodies in humans ... The time series of H1N1pdm09 antibodies from humans and swine show significant positive correlations.

Sample type: blood; serum

Citation context

References

53 references

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Publication metadata

Journal: Zoonoses and public health
Volume / Issue / Pages: 73 / 4 / 336-347
ISSN: 1863-2378
Journal country: Germany
DOI: 10.1111/zph.70051