ArticleVirology journal2024
Antigenic drift and immunity gap explain reduction in protective responses against influenza A(H1N1)pdm09 and A(H3N2) viruses during the COVID-19 pandemic: a cross-sectional study of human sera collected in 2019, 2021, 2022, and 2023.
Article in Virology journal, 2024. The graph could read no effect estimate from its abstract, so it casts no vote on the map. An erratum has been issued. Cited by 17 papers.
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17 citing papers in PubMed, 16 citations in OpenAlex.
- Phylodynamic reconstruction of H1N1pdm09 influenza virus transmission in Brazil: a decade of evolutionary dynamics.Emerging microbes & infections · 2026Article
- Hospitalisations for respiratory tract infections in preterm and term born children aged 1-5 years before, during and after COVID-19 control measures: an interrupted time-series analysis.BMJ paediatrics open · 2026Article
- Assessment of human immunity to A/H3N2 influenza subclade K during 2025 emergence.EBioMedicine · 2026Article
- 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.Zoonoses and public health · 2026Article
- Hospitalized children with influenza virus: a 17 year-long observational study including the 2009 H1N1 influenza pandemic and COVID-19 pandemic.BMC infectious diseases · 2026Observational
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- Favorable safety and immunogenicity of a combined quadrivalent influenza and recombinant SARS-CoV-2 vaccine in Sprague-Dawley rats for both primary and booster immunization.Frontiers in immunology · 2026Article
- Converging threats: The intersection of seasonal influenza surges and zoonotic highly pathogenic avian influenza.Global health & medicine · 2025Article
- Distinct Clinical Phenotypes of Severe Pediatric Influenza in the Post-COVID-19 Era: Insights from a Multicenter PICU Study in Türkiye.Children (Basel, Switzerland) · 2025Article
- Multiplex serology reveals age-specific immunodynamics of respiratory pathogens in the wake of the COVID-19 pandemic.Nature communications · 2025Article
- Assessing vaccine coverage and delivery strategies for influenza and COVID-19 among Italian healthcare workers: A 2015-2023 case study.Human vaccines & immunotherapeutics · 2025Article
- Excess Respiratory Hospitalisations Associated with Influenza, Respiratory Syncytial Virus and SARS-CoV-2 in Singapore from 2015 to 2023.Influenza and other respiratory viruses · 2025Article
- Multiplex serology reveals age-specific immunodynamics of endemic respiratory pathogens in the wake of the COVID-19 pandemic.medRxiv : the preprint server for health sciences · 2025Article
- Resurgence of common respiratory viruses and mycoplasma pneumoniae after ending the zero-COVID policy in Shanghai.Scientific reports · 2025Article
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Corrections and comments
- Erratum issued
Authors and funding
6 authors at 1 institution in 1 country.
Funding
No grant is acknowledged in the PubMed record.
Abstract
backgroundNon-pharmaceutical interventions implemented during the COVID-19 pandemic resulted in a marked reduction in influenza infections globally. The absence of influenza has raised concerns of waning immunity, and potentially more severe influenza seasons after the pandemic.
methodsTo evaluate immunity towards influenza post-COVID-19 pandemic we have assessed influenza A epidemics in Norway from October 2016 to June 2023 and measured antibodies against circulating strains of influenza A(H1N1)pdm09 and A(H3N2) in different age groups by hemagglutination inhibition (HAI) assays in a total of 3364 serum samples collected in 2019, 2021, 2022 and 2023.
resultsInfluenza epidemics in Norway from October 2016 until June 2023 were predominately influenza As, with a mixture of A(H1N1)pdm09 and A(H3N2) subtype predominance. We did not observe higher numbers of infections during the influenza epidemics following the COVID-19 pandemic than in pre-COVID-19 seasons. Frequencies of protective HAI titers against A(H1N1)pdm09 and A(H3N2) viruses were reduced in sera collected in 2021 and 2022, compared to sera collected in 2019. The reduction could, however, largely be explained by antigenic drift of new virus strains, as protective HAI titers remained stable against the same strain from one season to the next. However, we observed the development of an immunity gap in the youngest children during the pandemic which resulted in a prominent reduction in HAI titers against A(H1N1)pdm09 in 2021 and 2022. The immunity gap was partially closed in sera collected in 2023 following the A(H1N1)pdm09-dominated influenza seasons of 2022/2023. During the 2022/2023 epidemic, drift variants of A(H1N1)pdm09 belonging to the 5a.2a.1 clade emerged, and pre-season HAI titers were significantly lower against this clade compared to the ancestral 5a.2 clade.
conclusionThe observed reduction in protective antibodies against A(H1N1)pdm09 and A(H3N2) viruses post COVID-19 is best explained by antigenic drift of emerging viruses, and not waning of antibody responses in the general population. However, the absence of influenza during the pandemic resulted in an immunity gap in the youngest children. While this immunity gap was partially closed following the 2022/2023 influenza season, children with elevated risk of severe infection should be prioritized for vaccination.
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