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Background. Identifying an immunological correlate of protection for rotavirus vaccines (Rotarix [RV1] and RotaTeq [RV5]) would substantially facilitate testing of interventions for improving efficacy in developing countries and evaluating additional candidate rotavirus vaccines.Methods. We accessed PubMed and ClinicalTrials.gov to identify immunogenicity and efficacy trials for RV1 and RV5 to correlate anti-rotavirus serum immunoglobulin A (IgA) antibody titers vs efficacy in regions stratified by all-cause under-5 mortality rates (u5MR). We established a cutoff point for IgA geometric mean concentration or titer (GMC) that predicted lower efficacy and calculated pooled vaccine efficacy among countries with high vs low IgA titers.Findings. We observed an inverse correlation between u5MR and IgA titers for RV1 (r2 = 0.72; P < .001 and RV5 (r2 = 0.66; P < .001) and between efficacy and IgA titers for both vaccines (r2 = 0.56; P = .005). Postimmunization anti-rotavirus IgA GMC <90 were associated with decline in vaccine efficacy. Efficacy during first 2 years of life was significantly lower among countries with IgA GMC < 90 (44%; 95% confidence interval [CI], 30–55) compared to countries with GMC > 90 (85%; 95% CI, 82–88).Interpretation. We observed a significant correlation between IgA titers and rotavirus vaccine efficacy and hypothesize that a critical level of IgA antibody titer is associated with a sufficient level of sustained protection after rotavirus vaccination. [ABSTRACT FROM AUTHOR]