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Serum antibodies play an important role in natural protection from rotavirus infection and disease, but conflicting estimates of association have emerged from epidemiological studies in different geographical settings. In this study, we aim to assess the relationship between pre-existing serum immunoglobulin (Ig)G and IgA titers with protection against rotavirus infection and disease in a birth cohort of Indian children. Children were recruited at birth and followed up for 36 months. Stool samples were collected every 2 weeks and during episodes of diarrhea and serum samples were obtained at least every 6 months. The incidence rate of rotavirus infection and diarrhea was 0.9 (95% CI: 0.88, 0.99) and 0.2 (95% CI: 0.19, 0.25) episodes per child year, respectively. The risk of rotavirus infection and diarrhea decreased with age, while antibody titers (IgG and IgA) increased with age. After adjusting for age and number of previous infections, higher levels of IgG and IgA were independently associated with reduced risk of rotavirus infection. However, we did not find a clear association of IgG or IgA with rotavirus diarrhea risk or a threshold level of protection. The study supports a correlation of serum antibodies in reducing the risk of rotavirus infections, however the potential of serum antibody titer as a correlate of protection is not clear for children in lower income settings. [ABSTRACT FROM AUTHOR]

The authors explore the importance of birth cohorts in understanding norovirus infection, epidemiology and immunity. They note on the importance of birth cohort studies in understanding the acquisition of protective immunity against a pathogen. They mention a birth cohort study in Mexico which showed that severe disease is restricted to the first 2 infections, that each infection reduces future disease risk.

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]