Effects of age and birth cohort on influenza A virus subtype-specific hospitalization rates, United States 2010-2025
BACKGROUND: Older individuals (≥65 years) are at greatest risk of severe influenza requiring hospitalization. Since 2009, influenza-associated hospitalization rates during A(H1N1)pdm09-predominant influenza seasons have been lower than during A(H3N2) -predominant seasons. \. METHODS: Using laboratory-confirmed influenza hospitalization rates from U.S. population-based surveillance, we investigated the relative A(H1N1)pdm09 to A(H3N2) hospitalization rate ratios by patient year of age and birth cohort from 2010 through 2025. RESULTS: Results suggest partial protection against A(H1N1)pdm09 hospitalizations relative to A(H3N2) hospitalizations among patients born before 1945 (pre-1945 birth cohorts), and among individuals born during 1994 through 2009. Impact of partial protection against A(H1N1)pdm09-associated hospitalizations has diminished over time among older adults, contributing to elevated influenza hospitalization rates during the 2024-2025 influenza season. CONCLUSIONS: Our findings suggest that influenza A hospitalization rates may increase during future influenza seasons when both influenza A(H3N2) and A(H1N1) viruses circulate or following the emergence of novel A(H1N1)pdm09-like viruses.
Authors
- Pam Daily Kirley
- Kimberly Yousey‐Hindes (ORCID: https://orcid.org/0000-0002-9418-575X)
- Zachary Landis
- Manish R. Patel (ORCID: https://orcid.org/0000-0001-6836-2364)
- Khalil Harbi (ORCID: https://orcid.org/0000-0003-0449-0898)
- Brendan Flannery (ORCID: https://orcid.org/0000-0001-5041-308X)
- William Schaffner (ORCID: https://orcid.org/0000-0002-1375-8078)
- Maya Monroe
- Alicia Budd (ORCID: https://orcid.org/0000-0003-3936-164X)
- Kristen Olsen
- James Meek (ORCID: https://orcid.org/0000-0001-5553-1675)
- Brenda L. Tesini (ORCID: https://orcid.org/0000-0001-6051-0027)
- Dawud Ujamaa
- Mayvilynne Poblete
- Brian M. Gurbaxani (ORCID: https://orcid.org/0000-0002-9731-7359)
- H. Keipp Talbot (ORCID: https://orcid.org/0000-0003-0141-1760)
- Nicole Hood (ORCID: https://orcid.org/0000-0003-4031-3805)
- Nisha B. Alden (ORCID: https://orcid.org/0000-0002-8128-7714)
- Kyle P. Openo
- Krista Lung
- Bridget J. Anderson (ORCID: https://orcid.org/0000-0002-1233-3780)
- Rebecca Kondor (ORCID: https://orcid.org/0000-0002-2596-4282)
- Lauren Leegwater (ORCID: https://orcid.org/0000-0002-0888-7529)
- Lynnette Brammer
- Alicia M. Fry (ORCID: https://orcid.org/0000-0002-3208-9308)
- Adam Rowe
- Alissa O’Halloran
- Melissa Sutton (ORCID: https://orcid.org/0000-0001-8817-8724)
- Carrie Reed
- Deborah Aragon
- Ann Thomas
- L Witt
- Angiezel Merced-Morales
- Melanie Crossland
- Monica J Napoles
- Nancy E Moran
- Shikha Garg (ORCID: https://orcid.org/0009-0004-3493-2989)
- Cynthia Kenyon (ORCID: https://orcid.org/0000-0002-0441-293X)
- Ruth Lynfield
- Sarah Rojewski
- Patricia A Ryan
- Catherine Bozio
- Christina B Felsen
- Erica Wilson
Institutions
- New Mexico Department of Health (US)
- New York State Department of Health (US)
- Michigan Department of Health and Human Services (US)
- Colorado Department of Public Health and Environment (US)
- Oregon Health Authority (US)
- Emory University (US)
- National Center for Immunization and Respiratory Diseases (US)
- Chesapeake Public Schools (US)
- Lake County (US)
- Ohio Department of Health (US)
- Maryland Department of Health (US)
- North Carolina Division of Public Health (US)
- Georgia Department of Public Health (US)
- Minnesota Department of Health (US)
- University of Rochester (US)
- Vanderbilt University Medical Center (US)
Publication Details
- Journal
- The Journal of Infectious Diseases
- Published
- 2026-04-27
- DOI
- https://doi.org/10.1093/infdis/jiag232
- Primary Topic
- Influenza Virus Research Studies
- Type
- article
- Field-Weighted Citation Impact
- 0.00