tetano
Editor, Senior Moderator
J Infect Dis
. 2026 Apr 27:jiag232.
doi: 10.1093/infdis/jiag232. Online ahead of print.
Effects of age and birth cohort on influenza A virus subtype-specific hospitalization rates, United States 2010-2025
Alissa O'Halloran[SUP] 1 [/SUP], Nicole Hood[SUP] 1 [/SUP], Dawud Ujamaa[SUP] 1 2 [/SUP], Angiezel Merced-Morales[SUP] 1 [/SUP], Brian Gurbaxani[SUP] 1 [/SUP], Pam Daily Kirley[SUP] 3 [/SUP], Monica J Napoles[SUP] 3 [/SUP], Nisha B Alden[SUP] 4 [/SUP], Deborah Aragon[SUP] 4 [/SUP], James Meek[SUP] 5 [/SUP], Kimberly Yousey-Hindes[SUP] 5 [/SUP], Kyle P Openo[SUP] 6 7 [/SUP], Lucy S Witt[SUP] 6 7 [/SUP], Maya L Monroe[SUP] 8 [/SUP], Patricia A Ryan[SUP] 8 [/SUP], Lauren Leegwater[SUP] 9 [/SUP], Sarah Rojewski[SUP] 9 [/SUP], Cynthia Kenyon[SUP] 10 [/SUP], Ruth Lynfield[SUP] 10 [/SUP], Mayvilynne Poblete[SUP] 11 [/SUP], Zachary Q Landis[SUP] 11 [/SUP], Bridget J Anderson[SUP] 12 [/SUP], Adam J Rowe[SUP] 12 [/SUP], Christina B Felsen[SUP] 13 [/SUP], Brenda L Tesini[SUP] 13 [/SUP], Khalil Harbi[SUP] 14 [/SUP], Erica Wilson[SUP] 14 [/SUP], Krista Lung[SUP] 15 [/SUP], Nancy E Moran[SUP] 15 [/SUP], Melissa Sutton[SUP] 16 [/SUP], Ann Thomas[SUP] 16 [/SUP], H Keipp Talbot[SUP] 17 [/SUP], William Schaffner[SUP] 17 [/SUP], Melanie Crossland[SUP] 18 [/SUP], Kristen Olsen[SUP] 18 [/SUP], Manish Patel[SUP] 1 [/SUP], Alicia M Fry[SUP] 1 [/SUP], Rebecca Kondor[SUP] 1 [/SUP], Catherine Bozio[SUP] 1 [/SUP], Carrie Reed[SUP] 1 [/SUP], Lynnette Brammer[SUP] 1 [/SUP], Alicia Budd[SUP] 1 [/SUP], Brendan Flannery[SUP] 1 [/SUP], Shikha Garg[SUP] 1 [/SUP]
Affiliations
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.
Keywords: birth cohort; imprinting; influenza; influenza hospitalization; influenza virus.
. 2026 Apr 27:jiag232.
doi: 10.1093/infdis/jiag232. Online ahead of print.
Effects of age and birth cohort on influenza A virus subtype-specific hospitalization rates, United States 2010-2025
Alissa O'Halloran[SUP] 1 [/SUP], Nicole Hood[SUP] 1 [/SUP], Dawud Ujamaa[SUP] 1 2 [/SUP], Angiezel Merced-Morales[SUP] 1 [/SUP], Brian Gurbaxani[SUP] 1 [/SUP], Pam Daily Kirley[SUP] 3 [/SUP], Monica J Napoles[SUP] 3 [/SUP], Nisha B Alden[SUP] 4 [/SUP], Deborah Aragon[SUP] 4 [/SUP], James Meek[SUP] 5 [/SUP], Kimberly Yousey-Hindes[SUP] 5 [/SUP], Kyle P Openo[SUP] 6 7 [/SUP], Lucy S Witt[SUP] 6 7 [/SUP], Maya L Monroe[SUP] 8 [/SUP], Patricia A Ryan[SUP] 8 [/SUP], Lauren Leegwater[SUP] 9 [/SUP], Sarah Rojewski[SUP] 9 [/SUP], Cynthia Kenyon[SUP] 10 [/SUP], Ruth Lynfield[SUP] 10 [/SUP], Mayvilynne Poblete[SUP] 11 [/SUP], Zachary Q Landis[SUP] 11 [/SUP], Bridget J Anderson[SUP] 12 [/SUP], Adam J Rowe[SUP] 12 [/SUP], Christina B Felsen[SUP] 13 [/SUP], Brenda L Tesini[SUP] 13 [/SUP], Khalil Harbi[SUP] 14 [/SUP], Erica Wilson[SUP] 14 [/SUP], Krista Lung[SUP] 15 [/SUP], Nancy E Moran[SUP] 15 [/SUP], Melissa Sutton[SUP] 16 [/SUP], Ann Thomas[SUP] 16 [/SUP], H Keipp Talbot[SUP] 17 [/SUP], William Schaffner[SUP] 17 [/SUP], Melanie Crossland[SUP] 18 [/SUP], Kristen Olsen[SUP] 18 [/SUP], Manish Patel[SUP] 1 [/SUP], Alicia M Fry[SUP] 1 [/SUP], Rebecca Kondor[SUP] 1 [/SUP], Catherine Bozio[SUP] 1 [/SUP], Carrie Reed[SUP] 1 [/SUP], Lynnette Brammer[SUP] 1 [/SUP], Alicia Budd[SUP] 1 [/SUP], Brendan Flannery[SUP] 1 [/SUP], Shikha Garg[SUP] 1 [/SUP]
Affiliations
- PMID: 42044044
- DOI: 10.1093/infdis/jiag232
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.
Keywords: birth cohort; imprinting; influenza; influenza hospitalization; influenza virus.