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Immune history shapes human antibody responses to H5N1 influenza viruses

Nature Medicine volume 31, pages 1454–1458 (2025)Cite this article

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Abstract

Avian H5N1 influenza viruses are circulating widely in cattle and other mammals and pose a risk for a human pandemic. Previous studies suggest that older humans are more resistant to H5N1 infections due to childhood imprinting with other group 1 viruses (H1N1 and H2N2); however, the immunological basis for this is incompletely understood. Here we measured H5N1 antibody responses in sera from 157 individuals born between 1927 and 2016. We show that antibody titers to historical and recent H5N1 strains are highest in older individuals and correlate more strongly with birth year than with age, consistent with immune imprinting. Young children, who were likely not yet exposed to seasonal influenza viruses, had low levels of H5-specific antibodies. We also measured H5N1 antibody responses in sera from 100 individuals before and after receiving an A/Vietnam/1203/2004 H5N1 vaccine. We found that both younger and older humans produced H5-reactive antibodies to the A/Vietnam/1203/2004 vaccine strain and to a contemporary clade 2.3.4.4b strain, with higher seroconversion rates in young children who had lower levels of antibodies before vaccination. These studies suggest that younger individuals might benefit more from vaccination than older individuals in the event of an H5N1 pandemic.

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Fig. 1: Group 1 immune imprinting primes robust H5-reactive antibody responses.
Fig. 2: H5-reactive antibody levels correlate better with birth year than age.

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Data availability

All data are shown in the main figures and the Extended Data. Source data are provided with this paper.

Code availability

Code implementing the analyses is available at https://github.com/cobeylab/H5_titers_vs_imprinting.

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Acknowledgements

We thank the Penn Medicine BioBank and Children’s Hospital of Philadelphia as a resource for obtaining serum from humans with different birth years. We thank the NIAID and the VTEU clinical study teams from DMID 04-063, DMID 04-076 and DMID04-0077 for providing serum samples from clinical studies. This project was funded in part with federal funds from the National Institute of Allergy and Infectious Diseases, National Institutes of Health, Department of Health and Human Services, under contract no. 75N93021C00015 (S.E.H., S. Cobey and S. Cherry) and grant number R01AI08686 (S.E.H.). S.E.H. holds an Investigators in the Pathogenesis of Infectious Disease Award from the Burroughs Wellcome Fund.

Author information

Author notes

  1. These authors contributed equally: Tyler A. Garretson, Jiaojiao Liu, Shuk Hang Li, Gabrielle Scher, Jefferson J. S. Santos.

Authors and Affiliations

  1. Department of Microbiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA

    Tyler A. Garretson, Jiaojiao Liu, Shuk Hang Li, Gabrielle Scher, Jefferson J. S. Santos, Colleen Furey, Reilly K. Atkinson, Naiqing Ye, Jordan T. Ort, Kevin A. Hernandez, Theresa Eilola & Scott E. Hensley

  2. Department of Pathology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA

    Glenn Hogan & Sara Cherry

  3. Department of Ecology and Evolution, the University of Chicago, Chicago, IL, USA

    Marcos Costa Vieira, Kangchon Kim & Sarah Cobey

  4. Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA

    David C. Schultz

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  1. Tyler A. Garretson
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Contributions

S.E.H., T.A.G., J.L., S.H.L., G.S., C.F. and J.J.S.S. designed experiments. T.A.G., J.L., S.H.L., G.S., J.J.S.S., G.H., C.F., R.K.A., N.Y., J.T.O., K.A.H. and T.E. completed experiments and analyzed data. K.K., M.C.V. and S. Cobey performed modeling studies. S.E.H. wrote the paper, and all authors contributed to editing the paper. D.C.S., S. Cherry, S. Cobey and S.E.H. supervised experiments and data analyses. S.E.H. obtained funding for the study.

Corresponding author

Correspondence to Scott E. Hensley.

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Competing interests

S.E.H. is a co-inventor on patents that describe the use of nucleoside-modified mRNA as a vaccine platform. S.E.H. reports receiving consulting fees from Sanofi, Pfizer, Lumen, Novavax and Merck. T.A.G. was an employee of the University of Pennsylvania when the work was completed and is now an employee of GSK. The authors declare no other competing interests.

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Extended data

Extended Data Fig. 1 Imprinting probabilities of influenza subtypes by year of birth.

Probabilities that an individual was 1st exposed (that is ‘imprinted’) in childhood with an (a) H1N1 virus, an (b) H2N2 virus, (c) group 1 viruses (H1N1 or H2N2), or an (d) H3N2 virus based on their year of birth. Birth year-specific probabilities of immune imprinting to different influenza subtypes were generated using the methods described in Gostic et al.18 and the imprinting R package40.

Extended Data Fig. 2 Group 1 immune imprinting primes antibodies that cross-react to 2.3.4.4b H5N1 isolate currently circulating in cattle.

Sera samples were collected from healthy individuals (n = 157) at the Hospital of the University of Pennsylvania and Children’s Hospital of Philadelphia in 2017 and we quantified IgG binding to clade 2.3.4.4b A/Dairy Cattle/Texas/24-008749-002-v/2024 full length H5 HA. Vertical dashed lines mark years of the 1957 H2N2 and 1968 H3N2 pandemics and 1977 reemergence of H1N1. Each circle represents a geometric mean antibody titer in serum from a single individual from two independent replicates. Trend lines are locally estimated scatterplot smoothing (LOESS) curves (smoothing parameter = 0.4, degree = 2) with 95% CIs.

Source data

Extended Data Fig. 3 Most humans possess low levels of neutralizing antibodies against clade 1 and clade 2.3.4.4b H5N1.

Sera samples were collected from healthy individuals (n = 157) at the Hospital of the University of Pennsylvania and Children’s Hospital of Philadelphia in 2017 and we performed neutralization assays using conditionally replicative viruses expressing the HAs from (a) clade 1 A/Vietnam/1203/2004 and (b) clade 2.3.4.4b A/Pheasant/New York/22-009066-011/2022. Neutralizing titers are reported as reciprocal dilutions of serum that inhibit 90% of virus infection (NT90). Vertical dashed lines mark years of the 1957 H2N2 and 1968 H3N2 pandemics and 1977 reemergence of H1N1. Each circle represents a geometric mean antibody titer in serum from a single individual from two independent replicates. Trend lines are locally estimated scatterplot smoothing (LOESS) curves (smoothing parameter = 0.4, degree = 2) with 95% CIs.

Source data

Extended Data Fig. 4 H5N1 vaccination elicits strong H5 stalk-reactive antibodies in children.

Sera samples were obtained from participants (n = 100) before (day 0) and 28 days after receiving a first and second dose of an unadjuvanted A/Vietnam/1203/2004 H5N1 vaccine in 2005-2006. We quantified IgG binding to a ‘headless’ A/Vietnam/1203/2004 H5 stalk (a-c), and we calculated titer fold change by dividing day 28 post-boost titers by day 0 titers (d). We also measured antibody binding and fold change to clade 1 A/Vietnam/1203/2004 full length H5 HA (e-h) and clade 2.3.4.4b A/Pheasant/New York/22-009066-011/2022 full length H5 HA (i-l). Vertical dashed lines mark years of the 1957 H2N2 and 1968 H3N2 pandemics and 1977 reemergence of H1N1. Each circle represents a geometric mean antibody titer in serum from a single individual from two independent replicates. Samples from adults are grey and children are blue. Trend lines are locally estimated scatterplot smoothing (LOESS) curves (smoothing parameter = 0.4, degree = 2) with 95% CIs, fitted to adult samples.

Source data

Extended Data Fig. 5 H5N1 vaccination elicits antibodies that efficiently neutralize vaccine virus and mediate ADCC to matched and mismatched H5N1 viruses.

Sera samples were obtained from participants (n = 100) before (day 0) and 28 days after receiving a first and second dose of an unadjuvanted A/Vietnam/1203/2004 H5N1 vaccine in 2005-2006. We quantified levels of antibodies that neutralized virus with a clade 1 A/Vietnam/1203/2004 H5 HA (a-d) and clade 2.3.4.4b A/Pheasant/New York/22-009066-011/2022 H5 HA (e-h). Neutralizing titers are reported as reciprocal dilutions of serum that inhibit 90% of virus infection (NT90). We quantified levels of antibodies that mediated antibody-dependent cellular cytotoxicity (ADCC) with HAs from a clade 1 A/Vietnam/1203/2004 H5N1 virus (i-l) and a clade 2.3.4.4b A/Pheasant/New York/22-009066-011/2022 H5N1 virus (m-p). Fold change in panels d, h, l, and p were calculated by dividing day 28 post-boost values by day 0 values. Samples that did not have neutralizing antibodies were assigned a value of 10. Each circle represents a geometric mean antibody titer in serum from a single individual from two independent replicates. Samples from adults are grey and children are blue. Trend lines are locally estimated scatterplot smoothing (LOESS) curves (smoothing parameter = 0.4, degree = 2) with 95% CIs, fitted to adult samples.

Source data

Extended Data Table 1 Spearman correlation of antibody titers and influenza subtype imprinting probabilities in healthy individuals
Full size table
Extended Data Table 2 Comparison of post-vaccination fold changes in antibody titers between children and adults
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Extended Data Table 3 Model selection comparing the associations of age, birth year and imprinting probabilities with antibody levels to each antigen
Full size table
Extended Data Table 4 Bootstrapping analysis comparing how strongly different predictors correlate with titers to each antigen
Full size table
Extended Data Table 5 Information on human samples used in this study
Full size table

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Garretson, T.A., Liu, J., Li, S.H. et al. Immune history shapes human antibody responses to H5N1 influenza viruses. Nat Med 31, 1454–1458 (2025). https://doi.org/10.1038/s41591-025-03599-6

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