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.

PMID41857313 DOI10.1111/zph.70051 Year2026 Journal Zoonoses and public health Zoonoses Public Health Languageeng Statusppublish

Abstract

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.

Supporting text Virus Host Location

geometric mean titre 1 H1N1pdm09 3 Norway 6 seroprevalence 32 swine influenza 7 vaccine coverage 1 Antibodies, Viral 212 Influenza A Virus, H1N1 Subtype 74 Influenza Vaccines 20 Influenza, Human 286 Orthomyxoviridae Infections 228 Swine Diseases 153 Animals 1948 Cross-Sectional Studies 35 Humans 1440 Norway 6 Retrospective Studies 18 Seroepidemiologic Studies 113 Swine 258

Evidence records

3 total

Zoonotic Surveillance

3 records · 2 evidence types

Evidence type Serological Evidence

2 records

OVE10707 Serological Evidence

Key finding

Influenza A(H1N1)pdm09 antibodies were detected in unvaccinated swine across Norwegian counties during 2009/2010–2022/2023, indicating serological 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.

Method: antibody detection | serological assay | geometric mean titre (GMT)
Sample type: serum samples

OVE10709 Serological Evidence

Key finding

Temporal correlation of influenza A(H1N1)pdm09 antibody prevalence between humans and swine in Norway suggests possible bidirectional spillover at the swine–human interface.

Virus

Host

Location

Supporting text

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. 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.

Method: negative binomial regression | antibody seroprevalence analysis | geometric mean titre (GMT) time-series correlation

Evidence type Reservoir Ecology

1 records

OVE10710 Reservoir Ecology

Key finding

Swine are identified as potential epidemiological bridges and reservoirs supporting the emergence and circulation of novel zoonotic influenza A viruses with pandemic potential.

Virus

Host

Location

Supporting text

Swine may act as 'epidemiological bridges' and reservoirs for the emergence of novel zoonotic influenza viruses with pandemic potential.

Method: ecological interpretation based on cross-sectional serological data

References

53 references

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