Influenza Vaccine Effectiveness Against Medically Attended Outpatients Illness, United States, 2023-2024 Season

US Flu VE Network Investigators

doi:10.1093/cid/ciae658

Influenza Vaccine Effectiveness Against Medically Attended Outpatients Illness, United States, 2023-2024 Season

US Flu VE Network Investigators

Research output: Contribution to journal › Article › peer-review

7 Scopus citations

Abstract

Background The 2023-2024 US influenza season was characterized by a predominance of A(H1N1)pdm09 virus circulation with cocirculation of A(H3N2) and B/Victoria viruses. We estimated vaccine effectiveness (VE) in the United States against mild-to-moderate medically attended influenza illness in the 2023-2024 season. Methods We enrolled outpatients aged ≥8 months with acute respiratory illness in 7 states. Respiratory specimens were tested for influenza type/subtype by reverse-transcriptase polymerase chain reaction. Influenza VE was estimated with a test-negative design comparing odds of testing positive for influenza among vaccinated versus unvaccinated participants. We estimated VE by virus subtype/lineage and A(H1N1)pdm09 genetic subclades. Results Among 6629 enrolled patients, 1780 (27%) tested positive for influenza, including 806 with A(H1N1)pdm09, 567 with B/Victoria, and 328 with A(H3N2). VE against any influenza illness was 44% (95% confidence interval, 36%-51%): 29% (15%-41%) against influenza A(H1N1)pdm09, 74% (65%-81%) against B/Victoria, and 30% (8%-47%) against A(H3N2). Statistically significant protection against any influenza was found for all age groups except adults aged 50-64 years. Lack of protection in this age group was specific to influenza A-associated illness. We observed differences in VE by birth cohort and A(H1N1)pdm09 virus genetic subclade. Conclusions Vaccination reduced outpatient medically attended influenza overall by 44% and provided protection overall against circulating influenza A and B viruses. Serologic studies would help inform differences observed by age groups.

Original language	English
Pages (from-to)	e184-e191
Journal	Clinical Infectious Diseases
Volume	81
Issue number	4
DOIs	https://doi.org/10.1093/cid/ciae658
State	Published - Oct 15 2025

Keywords

case control
influenza
test-negative design
vaccination
vaccine effectiveness

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10.1093/cid/ciae658

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@article{7d3453fc978f48ad81d2bae49b16fd18,

title = "Influenza Vaccine Effectiveness Against Medically Attended Outpatients Illness, United States, 2023-2024 Season",

abstract = "Background The 2023-2024 US influenza season was characterized by a predominance of A(H1N1)pdm09 virus circulation with cocirculation of A(H3N2) and B/Victoria viruses. We estimated vaccine effectiveness (VE) in the United States against mild-to-moderate medically attended influenza illness in the 2023-2024 season. Methods We enrolled outpatients aged ≥8 months with acute respiratory illness in 7 states. Respiratory specimens were tested for influenza type/subtype by reverse-transcriptase polymerase chain reaction. Influenza VE was estimated with a test-negative design comparing odds of testing positive for influenza among vaccinated versus unvaccinated participants. We estimated VE by virus subtype/lineage and A(H1N1)pdm09 genetic subclades. Results Among 6629 enrolled patients, 1780 (27\%) tested positive for influenza, including 806 with A(H1N1)pdm09, 567 with B/Victoria, and 328 with A(H3N2). VE against any influenza illness was 44\% (95\% confidence interval, 36\%-51\%): 29\% (15\%-41\%) against influenza A(H1N1)pdm09, 74\% (65\%-81\%) against B/Victoria, and 30\% (8\%-47\%) against A(H3N2). Statistically significant protection against any influenza was found for all age groups except adults aged 50-64 years. Lack of protection in this age group was specific to influenza A-associated illness. We observed differences in VE by birth cohort and A(H1N1)pdm09 virus genetic subclade. Conclusions Vaccination reduced outpatient medically attended influenza overall by 44\% and provided protection overall against circulating influenza A and B viruses. Serologic studies would help inform differences observed by age groups.",

keywords = "case control, influenza, test-negative design, vaccination, vaccine effectiveness",

author = "\{US Flu VE Network Investigators\} and Chung, \{Jessie R.\} and Price, \{Ashley M.\} and Zimmerman, \{Richard K.\} and \{Moehling Geffel\}, Krissy and House, \{Stacey L.\} and Tara Curley and Wernli, \{Karen J.\} and Phillips, \{C. Hallie\} and Martin, \{Emily T.\} and Vaughn, \{Ivana A.\} and Vel Murugan and Matthew Scotch and Saade, \{Elie A.\} and Faryar, \{Kiran A.\} and Manjusha Gaglani and Ramm, \{Jason D.\} and Williams, \{Olivia L.\} and Walter, \{Emmanuel B.\} and Kirby, \{Marie K.\} and Keong, \{Lisa M.\} and Rebecca Kondor and Ellington, \{Sascha R.\} and Brendan Flannery and Kelly Conard and Bradley Bobbett and Hou, \{Ching Wen\} and Lucy Sublasky-Rodriguez and Holland, \{La Rinda\} and Izamar Garcia and Giavanna Caruth and Alexis Thomas and \{Hernandez Barrera\}, Gabrielle and Jesus Estrada and Yeager, \{Karen M.\} and Raquel Salgado and Martine Desulme and Bryan Remuto and Amanda McKillop and Britan Fairall and Ashley Graves and Martha Zayed and Marcus Volz and Kimberley Walker and Tora Adams and Jenica Aldas and Vanessa Crumpton and Erica Hayes and Paula Harkins and Victoria Harkins-Walston and Maria Lopez and Arnesa Pepino and Seretha Wallace and Sharla Russell and \{Da Graca\}, Briget and Muralidhar Jatla and Madhava Beeram and Tresa McNeal and Keith Stone and Arundhati Rao and Manohar Mutnal and Tammy Fisher and Jason Ettlinger and Courtney Shaver and Monica Bennett and Elisa Priest and Jennifer Thomas and Javed Butler and Alejandro Arroliga and Kate Castillo and Katherine Chen and Joe Choe and Todd Corder and Jana Ffitch and Victor Garcia and Miriam Marcus-Smith and Kathryn Moser and Sherry Kubitz and Stephanie Pimienta and Magali Sanchez and Paul Thottingal and Brian Williamson and Ishraaq Atkins and Sarita Baranwal and Isabelle Birt and Shane Bole and Jaleesa Clark and Marwa Hussein and Jacoby Jennings and Emiliegh Johnson and Anne Kaniclides and Armanda Kimberly and Regina Lehmann and Janay Patterson and Dolapo Raji and Maanasa Ravishankar and Leo Sullivan and Rachel Truscon and Ian Schamburg and Jessica Zvanut and Minh Nguyen and Jeremy Russell and Nichole Smith and Allison Hardin and Sarah Pruett-Welsh and Vidhya Venkataraman and Taylor Kristicevich and Leah Heath and Elise Blanke and Jamie Garner and Wykita Willis-Lockhart and Heena Khan and Rianna Robinson and Joanna Kramer and Mehal Patel and Lora Nordstrom and Mary Mulrow and Steven Holland and Faleye, \{Temitope O.C.\} and Monto, \{Arnold S.\} and Donny Hearn and Cheng, \{Caroline K.\} and Lois Lamerato and Lava, \{Jean Ashley\} and Muniza Hossain and Michael Lehmkuhl and Elizabeth Capasso-Gulve and Jamie Mills and Joshua Jackson and Bontrager, \{Natalie A.B.\} and Morrow, \{Darren J.\} and Wes Rountree and Todd, \{Christopher A.\} and Wolfe, \{Cameron R.\} and Salata, \{Robert A.\} and Stiffler, \{Kirk A.\} and Glagola, \{Jason J.\} and Zainab Albar and Christopher Ladikos and Donskey, \{Curtis J.\} and Nowalk, \{Mary Patricia\} and Balasubramani, \{G. K.\} and Tracey Conti and Figucia, \{David A.\} and Williams, \{John V.\} and Alexandra Weissman and Spencer Rose and Michael Smith and Leah Odame-Bamfo and Kempapura Murthy and Chandni Raiyani and Mufaddal Mamawala and Erika Kiniry and Brianna Wickersham and Rachael Doud and Matthew Nguyen and Juliana DaSilva and Sheffield, \{Sydney R.\} and Frederick, \{Julia C.\} and Wilson, \{Malania M.\} and Ewelina Lyszkowicz and Philip Shirk",

note = "Publisher Copyright: {\textcopyright} 2025 Published by Oxford University Press on behalf of Infectious Diseases Society of America.",

year = "2025",

month = oct,

day = "15",

doi = "10.1093/cid/ciae658",

language = "English",

volume = "81",

pages = "e184--e191",

journal = "Clinical Infectious Diseases",

issn = "1058-4838",

number = "4",

}

TY - JOUR

T1 - Influenza Vaccine Effectiveness Against Medically Attended Outpatients Illness, United States, 2023-2024 Season

AU - US Flu VE Network Investigators

AU - Chung, Jessie R.

AU - Price, Ashley M.

AU - Zimmerman, Richard K.

AU - Moehling Geffel, Krissy

AU - House, Stacey L.

AU - Curley, Tara

AU - Wernli, Karen J.

AU - Phillips, C. Hallie

AU - Martin, Emily T.

AU - Vaughn, Ivana A.

AU - Murugan, Vel

AU - Scotch, Matthew

AU - Saade, Elie A.

AU - Faryar, Kiran A.

AU - Gaglani, Manjusha

AU - Ramm, Jason D.

AU - Williams, Olivia L.

AU - Walter, Emmanuel B.

AU - Kirby, Marie K.

AU - Keong, Lisa M.

AU - Kondor, Rebecca

AU - Ellington, Sascha R.

AU - Flannery, Brendan

AU - Conard, Kelly

AU - Bobbett, Bradley

AU - Hou, Ching Wen

AU - Sublasky-Rodriguez, Lucy

AU - Holland, La Rinda

AU - Garcia, Izamar

AU - Caruth, Giavanna

AU - Thomas, Alexis

AU - Hernandez Barrera, Gabrielle

AU - Estrada, Jesus

AU - Yeager, Karen M.

AU - Salgado, Raquel

AU - Desulme, Martine

AU - Remuto, Bryan

AU - McKillop, Amanda

AU - Fairall, Britan

AU - Graves, Ashley

AU - Zayed, Martha

AU - Volz, Marcus

AU - Walker, Kimberley

AU - Adams, Tora

AU - Aldas, Jenica

AU - Crumpton, Vanessa

AU - Hayes, Erica

AU - Harkins, Paula

AU - Harkins-Walston, Victoria

AU - Lopez, Maria

AU - Pepino, Arnesa

AU - Wallace, Seretha

AU - Russell, Sharla

AU - Da Graca, Briget

AU - Jatla, Muralidhar

AU - Beeram, Madhava

AU - McNeal, Tresa

AU - Stone, Keith

AU - Rao, Arundhati

AU - Mutnal, Manohar

AU - Fisher, Tammy

AU - Ettlinger, Jason

AU - Shaver, Courtney

AU - Bennett, Monica

AU - Priest, Elisa

AU - Thomas, Jennifer

AU - Butler, Javed

AU - Arroliga, Alejandro

AU - Castillo, Kate

AU - Chen, Katherine

AU - Choe, Joe

AU - Corder, Todd

AU - Ffitch, Jana

AU - Garcia, Victor

AU - Marcus-Smith, Miriam

AU - Moser, Kathryn

AU - Kubitz, Sherry

AU - Pimienta, Stephanie

AU - Sanchez, Magali

AU - Thottingal, Paul

AU - Williamson, Brian

AU - Atkins, Ishraaq

AU - Baranwal, Sarita

AU - Birt, Isabelle

AU - Bole, Shane

AU - Clark, Jaleesa

AU - Hussein, Marwa

AU - Jennings, Jacoby

AU - Johnson, Emiliegh

AU - Kaniclides, Anne

AU - Kimberly, Armanda

AU - Lehmann, Regina

AU - Patterson, Janay

AU - Raji, Dolapo

AU - Ravishankar, Maanasa

AU - Sullivan, Leo

AU - Truscon, Rachel

AU - Schamburg, Ian

AU - Zvanut, Jessica

AU - Nguyen, Minh

AU - Russell, Jeremy

AU - Smith, Nichole

AU - Hardin, Allison

AU - Pruett-Welsh, Sarah

AU - Venkataraman, Vidhya

AU - Kristicevich, Taylor

AU - Heath, Leah

AU - Blanke, Elise

AU - Garner, Jamie

AU - Willis-Lockhart, Wykita

AU - Khan, Heena

AU - Robinson, Rianna

AU - Kramer, Joanna

AU - Patel, Mehal

AU - Nordstrom, Lora

AU - Mulrow, Mary

AU - Holland, Steven

AU - Faleye, Temitope O.C.

AU - Monto, Arnold S.

AU - Hearn, Donny

AU - Cheng, Caroline K.

AU - Lamerato, Lois

AU - Lava, Jean Ashley

AU - Hossain, Muniza

AU - Lehmkuhl, Michael

AU - Capasso-Gulve, Elizabeth

AU - Mills, Jamie

AU - Jackson, Joshua

AU - Bontrager, Natalie A.B.

AU - Morrow, Darren J.

AU - Rountree, Wes

AU - Todd, Christopher A.

AU - Wolfe, Cameron R.

AU - Salata, Robert A.

AU - Stiffler, Kirk A.

AU - Glagola, Jason J.

AU - Albar, Zainab

AU - Ladikos, Christopher

AU - Donskey, Curtis J.

AU - Nowalk, Mary Patricia

AU - Balasubramani, G. K.

AU - Conti, Tracey

AU - Figucia, David A.

AU - Williams, John V.

AU - Weissman, Alexandra

AU - Rose, Spencer

AU - Smith, Michael

AU - Odame-Bamfo, Leah

AU - Murthy, Kempapura

AU - Raiyani, Chandni

AU - Mamawala, Mufaddal

AU - Kiniry, Erika

AU - Wickersham, Brianna

AU - Doud, Rachael

AU - Nguyen, Matthew

AU - DaSilva, Juliana

AU - Sheffield, Sydney R.

AU - Frederick, Julia C.

AU - Wilson, Malania M.

AU - Lyszkowicz, Ewelina

AU - Shirk, Philip

PY - 2025/10/15

Y1 - 2025/10/15

N2 - Background The 2023-2024 US influenza season was characterized by a predominance of A(H1N1)pdm09 virus circulation with cocirculation of A(H3N2) and B/Victoria viruses. We estimated vaccine effectiveness (VE) in the United States against mild-to-moderate medically attended influenza illness in the 2023-2024 season. Methods We enrolled outpatients aged ≥8 months with acute respiratory illness in 7 states. Respiratory specimens were tested for influenza type/subtype by reverse-transcriptase polymerase chain reaction. Influenza VE was estimated with a test-negative design comparing odds of testing positive for influenza among vaccinated versus unvaccinated participants. We estimated VE by virus subtype/lineage and A(H1N1)pdm09 genetic subclades. Results Among 6629 enrolled patients, 1780 (27%) tested positive for influenza, including 806 with A(H1N1)pdm09, 567 with B/Victoria, and 328 with A(H3N2). VE against any influenza illness was 44% (95% confidence interval, 36%-51%): 29% (15%-41%) against influenza A(H1N1)pdm09, 74% (65%-81%) against B/Victoria, and 30% (8%-47%) against A(H3N2). Statistically significant protection against any influenza was found for all age groups except adults aged 50-64 years. Lack of protection in this age group was specific to influenza A-associated illness. We observed differences in VE by birth cohort and A(H1N1)pdm09 virus genetic subclade. Conclusions Vaccination reduced outpatient medically attended influenza overall by 44% and provided protection overall against circulating influenza A and B viruses. Serologic studies would help inform differences observed by age groups.

AB - Background The 2023-2024 US influenza season was characterized by a predominance of A(H1N1)pdm09 virus circulation with cocirculation of A(H3N2) and B/Victoria viruses. We estimated vaccine effectiveness (VE) in the United States against mild-to-moderate medically attended influenza illness in the 2023-2024 season. Methods We enrolled outpatients aged ≥8 months with acute respiratory illness in 7 states. Respiratory specimens were tested for influenza type/subtype by reverse-transcriptase polymerase chain reaction. Influenza VE was estimated with a test-negative design comparing odds of testing positive for influenza among vaccinated versus unvaccinated participants. We estimated VE by virus subtype/lineage and A(H1N1)pdm09 genetic subclades. Results Among 6629 enrolled patients, 1780 (27%) tested positive for influenza, including 806 with A(H1N1)pdm09, 567 with B/Victoria, and 328 with A(H3N2). VE against any influenza illness was 44% (95% confidence interval, 36%-51%): 29% (15%-41%) against influenza A(H1N1)pdm09, 74% (65%-81%) against B/Victoria, and 30% (8%-47%) against A(H3N2). Statistically significant protection against any influenza was found for all age groups except adults aged 50-64 years. Lack of protection in this age group was specific to influenza A-associated illness. We observed differences in VE by birth cohort and A(H1N1)pdm09 virus genetic subclade. Conclusions Vaccination reduced outpatient medically attended influenza overall by 44% and provided protection overall against circulating influenza A and B viruses. Serologic studies would help inform differences observed by age groups.

KW - case control

KW - influenza

KW - test-negative design

KW - vaccination

KW - vaccine effectiveness

UR - https://www.scopus.com/pages/publications/105021284965

U2 - 10.1093/cid/ciae658

DO - 10.1093/cid/ciae658

M3 - Article

C2 - 39761230

AN - SCOPUS:105021284965

SN - 1058-4838

VL - 81

SP - e184-e191

JO - Clinical Infectious Diseases

JF - Clinical Infectious Diseases

IS - 4

ER -

Influenza Vaccine Effectiveness Against Medically Attended Outpatients Illness, United States, 2023-2024 Season

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Keywords

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