{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"institution":[{"name":"medRxiv"}],"indexed":{"date-parts":[[2026,8,4]],"date-time":"2026-08-04T21:54:30Z","timestamp":1785880470728,"version":"3.56.0"},"posted":{"date-parts":[[2026,3,26]]},"group-title":"Epidemiology","reference-count":34,"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>We assessed associations between antibody concentrations within 7 days of symptom onset and testing positive for influenza virus infection among outpatients enrolled in a test-negative study.<\/jats:p>\n                <\/jats:sec>\n                <jats:sec>\n                  <jats:title>Methods<\/jats:title>\n                  <jats:p>From November 2018\u2500May 2019, study sites in five states obtained serum and respiratory specimens from outpatients aged \u226518 years presenting with acute respiratory illness. Respiratory specimens were tested for influenza virus, and viral clades were identified by genomic sequencing. We measured influenza antibody titers against vaccine and circulating viruses by hemagglutination inhibition (HI), microneutralization (MN) and neuraminidase inhibition (NAI) assays. Percent of patients with HI, MN and NAI titers \u226510 and \u226540 were compared among patients with and without influenza-associated illness, and reduction in odds of confirmed influenza at increasing HI, MN and NAI antibody titers was estimated using logistic regression adjusting for influenza vaccination status and time since beginning of influenza season.<\/jats:p>\n                <\/jats:sec>\n                <jats:sec>\n                  <jats:title>Results<\/jats:title>\n                  <jats:p>Among 175 patients with confirmed influenza virus infection, including 112 with influenza A(H1N1)pdm09 and 63 with A(H3N2) (44 clade 3C.3a), and 130 test-negative control patients, higher antibody titers against influenza hemagglutinin or neuraminidase proteins at enrollment were associated with lower odds of influenza virus infection. HI and MN antibody titers against circulating viruses were more strongly associated with protection than titers against vaccine reference viruses. Odds of A(H1N1)pdm09 infection were 44% and 54% lower for each two-fold increase in A(H1N1)pdm09 HI or NAI titer, respectively. Odds of A(H3N2) infection were 46% and 30% lower, respectively, for each two-fold increase in MN or NAI titer against circulating A(H3N2) virus clade. NAI titers were independently associated with lower odds of influenza A(H1N1)pdm09 and A(H3N2) after controlling for HI titer.<\/jats:p>\n                <\/jats:sec>\n                <jats:sec>\n                  <jats:title>Conclusion<\/jats:title>\n                  <jats:p>Higher influenza antibody titers against circulating viruses were associated with lower likelihood of influenza virus infection among adult patients with acute respiratory illness.<\/jats:p>\n                <\/jats:sec>\n                <jats:sec>\n                  <jats:title>SUMMARY<\/jats:title>\n                  <jats:p>From November 2018\u2500May 2019, we assessed the association between antibody concentrations during acute illness and laboratory-confirmed influenza among adult patients enrolled in a test-negative study in five US states. We found that higher influenza antibody titers were associated with lower likelihood of symptomatic influenza virus infection.<\/jats:p>\n                <\/jats:sec>","DOI":"10.64898\/2026.03.24.26349239","type":"posted-content","created":{"date-parts":[[2026,3,26]],"date-time":"2026-03-26T17:35:18Z","timestamp":1774546518000},"source":"Crossref","is-referenced-by-count":2,"title":["Influenza Antibody Levels Associated with Laboratory-Confirmed Influenza in a Test-Negative Study Design, US Flu VE Network, November 2018\u2013May 2019"],"prefix":"10.64898","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-5041-308X","authenticated-orcid":false,"given":"Brendan","family":"Flannery","sequence":"first","affiliation":[{"name":"Centers for Disease Control and Prevention, Atlanta, GA, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5205-966X","authenticated-orcid":false,"given":"Jessie 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Temple, TX, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0437-5179","authenticated-orcid":false,"given":"Kempapura","family":"Murthy","sequence":"additional","affiliation":[{"name":"Baylor Scott & White Health, Temple, TX, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5941-6092","authenticated-orcid":false,"given":"Richard K.","family":"Zimmerman","sequence":"additional","affiliation":[{"name":"University of Pittsburgh, Pittsburgh, PA, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1702-2690","authenticated-orcid":false,"given":"Mary Patricia","family":"Nowalk","sequence":"additional","affiliation":[{"name":"University of Pittsburgh, Pittsburgh, PA, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Michael L.","family":"Jackson","sequence":"additional","affiliation":[{"name":"Kaiser Permanente Washington Health Research Institute, Seattle, WA, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7945-0327","authenticated-orcid":false,"given":"Karen J.","family":"Wernli","sequence":"additional","affiliation":[{"name":"Kaiser Permanente Washington Health Research Institute, Seattle, WA, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3018-435X","authenticated-orcid":false,"given":"Arnold S.","family":"Monto","sequence":"additional","affiliation":[{"name":"University of Michigan School of Public Health, Ann Arbor, MI, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"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":"Huong Q.","family":"Nguyen","sequence":"additional","affiliation":[{"name":"Marshfield Clinic Research 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