{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"institution":[{"name":"medRxiv"}],"indexed":{"date-parts":[[2026,7,30]],"date-time":"2026-07-30T18:09:39Z","timestamp":1785434979501,"version":"3.56.0"},"posted":{"date-parts":[[2026,3,26]]},"group-title":"Epidemiology","reference-count":35,"publisher":"openRxiv","license":[{"start":{"date-parts":[[2026,3,26]],"date-time":"2026-03-26T00:00:00Z","timestamp":1774483200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"accepted":{"date-parts":[[2026,3,26]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                <jats:sec>\n                  <jats:title>Background<\/jats:title>\n                  <jats:p>Influenza A(H1N1)pdm09 and A(H3N2) viruses predominated during the 2024\u201325 U.S. influenza season. We estimated influenza vaccine effectiveness (VE) in the United States against mild-to-moderate outpatient influenza illness by influenza type and subtype in the 2024\u201325 season.<\/jats:p>\n                <\/jats:sec>\n                <jats:sec>\n                  <jats:title>Methods<\/jats:title>\n                  <jats:p>We enrolled outpatients aged \u22658 months with acute respiratory illness symptoms including cough in 7 states. Upper respiratory specimens were tested for influenza type\/subtype by reverse-transcriptase polymerase chain reaction (RT-PCR). Influenza VE was estimated with a test-negative design comparing odds of testing positive for influenza among vaccinated versus unvaccinated participants controlling for age, study site, underlying health status, and month of illness onset. We also estimated VE of current season vaccination among adults stratified by prior season vaccination status.<\/jats:p>\n                <\/jats:sec>\n                <jats:sec>\n                  <jats:title>Results<\/jats:title>\n                  <jats:p>Among 6,793 enrolled patients, 2,016 (30%) tested positive for influenza including 961 A(H3N2), 770 A(H1N1)pdm09, and 183 B\/Victoria. Overall vaccine effectiveness against any influenza illness was 33% (95% Confidence Interval [CI]: 24 to 41): 27% (95% CI: 14 to 39) against influenza A(H3N2), 37% (95% CI: 24 to 48) against A(H1N1)pdm09, and 40% (95% CI: 12 to 59) against B\/Victoria. VE did not differ based on whether or not participants had received influenza vaccine the previous season.<\/jats:p>\n                <\/jats:sec>\n                <jats:sec>\n                  <jats:title>Conclusions<\/jats:title>\n                  <jats:p>Influenza vaccination during the 2024\u201325 season protected against circulating influenza viruses, reducing the risk of outpatient medically attended influenza overall by approximately one-third among people who were vaccinated.<\/jats:p>\n                <\/jats:sec>\n                <jats:sec>\n                  <jats:title>Key Points<\/jats:title>\n                  <jats:p>Influenza vaccine reduced the risk of outpatient acute respiratory illness due to laboratory-confirmed influenza during the 2024\u201325 season by a third.<\/jats:p>\n                <\/jats:sec>","DOI":"10.64898\/2026.03.24.26348229","type":"posted-content","created":{"date-parts":[[2026,3,26]],"date-time":"2026-03-26T18:35:17Z","timestamp":1774550117000},"source":"Crossref","is-referenced-by-count":1,"title":["Influenza vaccine effectiveness against outpatient acute respiratory illness with laboratory-confirmed influenza, United States, 2024\u201325 season"],"prefix":"10.64898","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-5205-966X","authenticated-orcid":false,"given":"Jessie R.","family":"Chung","sequence":"first","affiliation":[{"name":"Influenza Division, US Centers for Disease Control and Prevention, Atlanta, GA, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ashley M.","family":"Price","sequence":"additional","affiliation":[{"name":"Influenza Division, US Centers for Disease Control and Prevention, Atlanta, GA, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Stacey L.","family":"House","sequence":"additional","affiliation":[{"name":"Washington University School of Medicine in St. Louis, Department of Emergency Medicine, St. Louis, MO, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jamie","family":"Mills","sequence":"additional","affiliation":[{"name":"Washington University School of Medicine in St. Louis, Department of Emergency Medicine, St. Louis, MO, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Karen J.","family":"Wernli","sequence":"additional","affiliation":[{"name":"Kaiser Permanente Washington Health Research Institute, Seattle, WA, USA"},{"name":"Kaiser Permanente Bernard J. Tyson School of Medicine, Pasadena, CA, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Magali","family":"Sanchez","sequence":"additional","affiliation":[{"name":"University of Washington, Department of Epidemiology, Seattle, WA, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5771-8895","authenticated-orcid":false,"given":"Emily T.","family":"Martin","sequence":"additional","affiliation":[{"name":"University of Michigan School of Public Health, Ann Arbor, MI, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ivana A.","family":"Vaughn","sequence":"additional","affiliation":[{"name":"Henry Ford Health, Department of Public Health Sciences, Detroit, MI, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7368-7742","authenticated-orcid":false,"given":"Vel","family":"Murugan","sequence":"additional","affiliation":[{"name":"Biodesign Center for Personalized Diagnostics, College of Health Solutions and Health Observatory, Arizona State University, Tempe, AZ"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Joanna","family":"Kramer","sequence":"additional","affiliation":[{"name":"Phoenix Children\u2019s Hospital, Phoenix, AZ"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Elie A.","family":"Saade","sequence":"additional","affiliation":[{"name":"University Hospitals Cleveland Medical Center, Case Western Reserve University School of Medicine, Cleveland, OH"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kiran","family":"Faryar","sequence":"additional","affiliation":[{"name":"University Hospitals Cleveland Medical Center, Case Western Reserve University School of Medicine, Cleveland, OH"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Manjusha","family":"Gaglani","sequence":"additional","affiliation":[{"name":"Baylor Scott & White Health, Temple, TX, 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