Vaccine Effectiveness Against Influenza A(H1N1), A(H3N2), and B-Associated Hospitalizations, United States, 1 September 2023 to 31 May 2024

Nathaniel M Lewis¹, Elizabeth J Harker¹, Seana Cleary¹, Yuwei Zhu², Carlos G Grijalva², James D Chappell², Jillian P Rhoads², Adrienne Baughman², Jonathan D Casey², Paul W Blair², Ian D Jones², Cassandra A Johnson², Natasha B Halasa², Adam S Lauring³, Emily T Martin³, Manju Gaglani^{4

5}, Shekhar Ghamande⁵, Cristie Columbus^{5

6}, Jay S Steingrub⁷, Abhijit Duggal⁸, Jamie R Felzer⁹, Matthew E Prekker¹⁰, Ithan D Peltan^{11

12}, Samuel M Brown^{11

12}, David N Hager¹³, Michelle N Gong¹⁴, Amira Mohamed¹⁴, Matthew C Exline¹⁵, Akram Khan¹⁶, Samantha A N Ferguson¹⁷, Jarrod Mosier¹⁸, Nida Qadir¹⁹, Steven Y Chang¹⁹, Adit A Ginde²⁰, Anne Zepeski²¹, Christopher Mallow²², Estelle S Harris¹¹, Nicholas J Johnson²³, Kevin W Gibbs²⁴, Jennie H Kwon²⁵, Ivana A Vaughn²⁶, Mayur Ramesh²⁷, Basmah Safdar²⁸, Diya Surie²⁹, Fatimah S Dawood²⁹, Sascha Ellington¹, Wesley H Self²

Affiliations

¹ Influenza Division, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.
² School of Medicine, Vanderbilt University, Nashville, Tennessee, USA.
³ Michigan Medicine, University of Michigan, Ann Arbor, Michigan, USA.
⁴ Section of Infectious Diseases, Baylor Scott and White Health, Temple, Texas, USA.
⁵ Center for Research in Vaccines and Infections, Baylor College of Medicine, Temple, Texas, USA.
⁶ College of Medicine, Texas A&M University, Dallas, Texas, USA.
⁷ Department of Critical Care Medicine, Baystate Medical Center, Springfield, Massachusetts, USA.
⁸ Department of Critical Care, Cleveland Clinic, Cleveland, Ohio, USA.
⁹ School of Medicine, Emory University, Atlanta, Georgia, USA.
¹⁰ Department of Emergency Medicine, Hennepin County Medical Center, Minneapolis, Minnesota, USA.
¹¹ School of Medicine, University of Utah, Salt Lake City, Utah, USA.
¹² Department of Pulmonary and Critical Care Medicine, Intermountain Medical Center, Murray, Utah, USA.
¹³ Department of Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
¹⁴ Montefiore Medical Center, Albert Einstein College of Medicine, New York, New York, USA.
¹⁵ Critical Care Department, Wexner Medical Center, The Ohio State University, Columbus, Ohio, USA.
¹⁶ Division of Pulmonary and Critical Care Medicine, School of Medicine, Oregon Health and Science University, Portland, Oregon, USA.
¹⁷ School of Medicine, Stanford University, Stanford, California, USA.
¹⁸ Department of Emergency Medicine, College of Medicine, University of Arizona, Tucson, Arizona, USA.
¹⁹ Ronald Reagan Medical Center, University of California, Los Angeles, Los Angeles, California, USA.
²⁰ Department of Emergency Medicine, University of Colorado School of Medicine, Aurora, Colorado, USA.
²¹ Department of Emergency Medicine, Carver College of Medicine, Iowa City, Iowa, USA.
²² Division of Pulmonary, Critical Care, and Sleep Medicine, University of Miami School of Medicine, Miami, Florida, USA.
²³ Department of Emergency Medicine, University of Washington, Seattle, Washington, USA.
²⁴ Department of Pulmonary, Critical Care, Allergy, and Immunologic Diseases, Wake Forest School of Medicine, Winston-Salem, North Carolina, USA.
²⁵ Department of Medicine, Washington University in St Louis, St Louis, Missouri, USA.
²⁶ Department of Public Health Sciences, Henry Ford Health, Detroit, Michigan, USA.
²⁷ Department of Internal Medicine/Infectious Diseases, Henry Ford Health, Detroit, Michigan, USA.
²⁸ Department of Emergency Medicine, Yale University School of Medicine, New Haven, Connecticut, USA.
²⁹ Division of COVID-19 and Other Respiratory Viral Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.

PMID: 40198276
DOI: 10.1093/infdis/jiaf185

Vaccine Effectiveness Against Influenza A(H1N1), A(H3N2), and B-Associated Hospitalizations, United States, 1 September 2023 to 31 May 2024

Nathaniel M Lewis et al. J Infect Dis. 2025.

. 2025 Oct 15;232(4):e626-e636.

doi: 10.1093/infdis/jiaf185.

Authors

Affiliations

¹ Influenza Division, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.
² School of Medicine, Vanderbilt University, Nashville, Tennessee, USA.
³ Michigan Medicine, University of Michigan, Ann Arbor, Michigan, USA.
⁴ Section of Infectious Diseases, Baylor Scott and White Health, Temple, Texas, USA.
⁵ Center for Research in Vaccines and Infections, Baylor College of Medicine, Temple, Texas, USA.
⁶ College of Medicine, Texas A&M University, Dallas, Texas, USA.
⁷ Department of Critical Care Medicine, Baystate Medical Center, Springfield, Massachusetts, USA.
⁸ Department of Critical Care, Cleveland Clinic, Cleveland, Ohio, USA.
⁹ School of Medicine, Emory University, Atlanta, Georgia, USA.
¹⁰ Department of Emergency Medicine, Hennepin County Medical Center, Minneapolis, Minnesota, USA.
¹¹ School of Medicine, University of Utah, Salt Lake City, Utah, USA.
¹² Department of Pulmonary and Critical Care Medicine, Intermountain Medical Center, Murray, Utah, USA.
¹³ Department of Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
¹⁴ Montefiore Medical Center, Albert Einstein College of Medicine, New York, New York, USA.
¹⁵ Critical Care Department, Wexner Medical Center, The Ohio State University, Columbus, Ohio, USA.
¹⁶ Division of Pulmonary and Critical Care Medicine, School of Medicine, Oregon Health and Science University, Portland, Oregon, USA.
¹⁷ School of Medicine, Stanford University, Stanford, California, USA.
¹⁸ Department of Emergency Medicine, College of Medicine, University of Arizona, Tucson, Arizona, USA.
¹⁹ Ronald Reagan Medical Center, University of California, Los Angeles, Los Angeles, California, USA.
²⁰ Department of Emergency Medicine, University of Colorado School of Medicine, Aurora, Colorado, USA.
²¹ Department of Emergency Medicine, Carver College of Medicine, Iowa City, Iowa, USA.
²² Division of Pulmonary, Critical Care, and Sleep Medicine, University of Miami School of Medicine, Miami, Florida, USA.
²³ Department of Emergency Medicine, University of Washington, Seattle, Washington, USA.
²⁴ Department of Pulmonary, Critical Care, Allergy, and Immunologic Diseases, Wake Forest School of Medicine, Winston-Salem, North Carolina, USA.
²⁵ Department of Medicine, Washington University in St Louis, St Louis, Missouri, USA.
²⁶ Department of Public Health Sciences, Henry Ford Health, Detroit, Michigan, USA.
²⁷ Department of Internal Medicine/Infectious Diseases, Henry Ford Health, Detroit, Michigan, USA.
²⁸ Department of Emergency Medicine, Yale University School of Medicine, New Haven, Connecticut, USA.
²⁹ Division of COVID-19 and Other Respiratory Viral Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.

PMID: 40198276
DOI: 10.1093/infdis/jiaf185

Abstract

Background: The 2023-2024 influenza season included sustained elevated activity from December 2023 to February 2024 and continued activity through May 2024. Influenza A(H1N1), A(H3N2), and B viruses circulated during the season.

Methods: During 1 September 2023 to 31 May 2024, a multistate sentinel surveillance network of 24 medical centers in 20 US states enrolled adults aged ≥18 years hospitalized with acute respiratory illness. Consistent with a test-negative design, cases tested positive for influenza viruses by molecular or antigen test, and controls tested negative for influenza viruses and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Vaccine effectiveness (VE) against influenza-associated hospitalization was calculated as (1 - adjusted odds ratio for vaccination) × 100%.

Results: Among 7690 patients, including 1170 influenza cases (33% vaccinated) and 6520 controls, VE was 40% (95% confidence interval [CI], 31%-48%) with varying estimates by age: 18-49 years, 53% (95% CI, 34%-67%); 50-64 years, 47% (95% CI, 31%-60%); ≥ 65 years, 31% (95% CI, 16%-43%). Protection was similar among immunocompetent patients (40%; 95% CI, 30%-49%) and immunocompromised patients (32%; 95% CI, 7%-50%). VE was statistically significant against influenza B (67%; 95% CI, 35%-84%) and A(H1N1) (36%; 95% CI, 21%-48%) and crossed the null against A(H3N2) (19%; 95% CI, -8% to 39%). VE was higher for patients 14-60 days from vaccination (54%; 95% CI, 40%-65%) than >120 days (18%; 95% CI, -1% to 33%).

Conclusions: During 2023-2024, influenza vaccination reduced the risk of influenza A(H1N1)- and influenza B-associated hospitalizations among adults; effectiveness was lower in patients vaccinated >120 days prior to illness onset compared with those vaccinated 14-60 days prior.

Keywords: hospitalization; seasonal influenza; severe influenza; vaccine effectiveness; waning.

Published by Oxford University Press on behalf of Infectious Diseases Society of America 2025.

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Conflict of interest statement

Potential conflicts of interest. J. D. C. reports research funding from Merck to study RSV epidemiology in hospitalized children with acute respiratory illness, outside the submitted work. M. G. reports funding from CDC for the US Flu VE Network and SYNERGY study; CDC-Abt Associates for RECOVER-PROTECT cohort studies; and CDC-Westat for the VISION study, outside the submitted work. M. N. G. reports being an advisor to trial design for Regeneron; participating as a Data and Safety Monitoring Board member for Best; receiving grants from National Heart, Lung, and Blood Institute (NHLBI) as a HART coinvestigator and Academic Strategic Planning Steering Committee; and institutional payments from Wolters Kluwer as Section Editor for UptoDate, outside the submitted work. C. G. G. has served as consultant for Merck and GSK; and received research support from CDC, National Institutes of Health (NIH), Food and Drug Administration, Agency for Healthcare Research and Quality, and SyneosHealth, outside the submitted work. N. B. H. reports receiving a grant from Merck; and participating on an advisory board for CSL-Seqirus, outside the submitted work. A. K. has received research support from 4D Medical, Roche Pharmaceuticals, Dompe Pharmaceuticals, Eli Lily, Direct Biologics and NIH, NHLBI, Biomedical Advanced Research and Development Authority, outside the submitted work. A. S. L. reports research support from National Institute of Allergy and Infectious Diseases, CDC, Michigan Department of Health and Human Services, and National Science Foundation; and consulting fees from Roche related to a clinical trial of baloxavir, outside of the submitted work. I. D. P. reports research support from the National Institute of General Medical Sciences (NIGMS), NHLBI and NIGMS; and funding to his institution from Bluejay Diagnostics and Novartis, outside the submitted work. M. R. served on an advisory board for Moderna and Pfizer; and was an unbranded speaker for AstraZeneca, outside the submitted work. I. A. V. receives funding through her institution from eMaxHealth, Lilly USA, and Evidera PPD, outside the submitted work. All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.

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Vaccine Effectiveness Against Influenza A(H1N1), A(H3N2), and B-Associated Hospitalizations, United States, 1 September 2023 to 31 May 2024

Affiliations

Vaccine Effectiveness Against Influenza A(H1N1), A(H3N2), and B-Associated Hospitalizations, United States, 1 September 2023 to 31 May 2024

Authors

Affiliations

Abstract

Conflict of interest statement

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