biostudies-literatureLim WWNational Institute of Allergy and Infectious DiseasesNIAID NIH HHSUS Centers for Disease Control and PreventionRGC Senior Research Fellow SchemeResearch Grants Council152-160https://www.ebi.ac.uk/biostudies/studies/S-EPMC11272062biostudies-literatureUnknown230(1)<h4>Background</h4>The hemagglutination inhibition antibody (HAI) titer contributes only a part of vaccine-induced protection against influenza virus infections. Using causal mediation analysis, we quantified the proportion of vaccine efficacy mediated by postvaccination HAI titers.<h4>Methods</h4>We conducted causal mediation analyses using data from a randomized, active-comparator controlled, phase III, trial of an inactivated, split-virion seasonal quadrivalent influenza vaccine in children conducted from October 2010 to December 2011 in 8 countries. Vaccine efficacy was estimated using a weighted Cox proportional hazards model. Estimates were decomposed into the direct and indirect effects mediated by postvaccination HAI titers.<h4>Results</h4>The proportions of vaccine efficacy mediatThe Journal of infectious diseasesHemagglutination Inhibition Antibody Titers as Mediators of Influenza Vaccine Efficacy Against Symptomatic Influenza A(H1N1), A(H3N2), and B/Victoria Virus Infections.PMC1127206275D301-23-C-17596T11-712/19-NR01 AI170116HKU SRFS2021-7S03Lim WWWong SSCowling BJFeng SSullivan SGfalseHemagglutination Inhibition Antibody Titers as Mediators of Influenza Vaccine Efficacy Against Symptomatic Influenza A(H1N1), A(H3N2), and B/Victoria Virus Infections.<h4>Background</h4>The hemagglutination inhibition antibody (HAI) titer contributes only a part of vaccine-induced protection against influenza virus infections. Using causal mediation analysis, we quantified the proportion of vaccine efficacy mediated by postvaccination HAI titers.<h4>Methods</h4>We conducted causal mediation analyses using data from a randomized, active-comparator controlled, phase III, trial of an inactivated, split-virion seasonal quadrivalent influenza vaccine in children conducted from October 2010 to December 2011 in 8 countries. Vaccine efficacy was estimated using a weighted Cox proportional hazards model. Estimates were decomposed into the direct and indirect effects mediated by postvaccination HAI titers.<h4>Results</h4>The proportions of vaccine efficacy mediat2024-01-01T00:00:00Z2024 Jul2026-06-03T01:26:16.556Z2025-04-06T22:20:54.544ZS-EPMC112720623905273410.1093/infdis/jiae122