Effects of Age and Birth Cohort on Influenza A Virus Subtype-Specific Hospitalization Rates, United States, 2010–2025
Year: 2026
Type: article
Study design: Observational Study
Abstract: 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 US 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 influenza A(H3N2) and A(H1N1) viruses circulate or following the emergence of novel A(H1N1)pdm09-like viruses.
Authors: Alissa O’Halloran, Nicole Hood, Dawud Ujamaa, Angiezel Merced-Morales, Brian Gurbaxani, Pam Daily Kirley, Monica J Napoles, Nisha B Alden, Deborah Aragon, James Meek, Kimberly Yousey-Hindes, Kyle P Openo, Lucy S Witt, Maya L Monroe, Patricia A Ryan, Lauren Leegwater, Sarah Rojewski, Cynthia Kenyon, Ruth Lynfield, Mayvilynne Poblete, Zachary Q Landis, Bridget J Anderson, Adam J Rowe, Christina B Felsen, Brenda L Tesini, Khalil Harbi, Erica Wilson, Krista Lung, Nancy E Moran, Melissa Sutton, Ann Thomas, H Keipp Talbot, William Schaffner, Melanie Crossland, Kristen Olsen, Manish Patel, Alicia M Fry, Rebecca Kondor, Catherine Bozio, Carrie Reed, Lynnette Brammer, Alicia Budd, Brendan Flannery, Shikha Garg
Institutions: Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases, Colorado Department of Public Health and Environment, Yale University, Emory University, Maryland Department of Health, Michigan Department of Health and Human Services, Minnesota Department of Health, New York State Department of Health, University of Rochester Medicine, University of Rochester, North Carolina Division of Public Health, Ohio Department of Health, Oregon Health Authority, Vanderbilt University Medical Center
Language: English
Subfield: Epidemiology
Field: Medicine
Domain: Health Sciences
Open Access status: green
Funders: National Foundation for Infectious Diseases, New York State Department of Health, Minnesota Department of Health, Yale University, Council of State and Territorial Epidemiologists, Infectious Diseases Society of America, Emory University, Colorado Department of Public Health and Environment, University of Rochester, Michigan Department of Health and Human Services, Ohio Department of Health, Vanderbilt University Medical Center, Centers for Disease Control and Prevention, School of Medicine, Emory University, Abbott Diagnostics
OpenAlex ID: W7155857372