Rotavirus-Specific Immunoglobulin A Responses Are Impaired and Serve as a Suboptimal Correlate of Protection Among Infants in Bangladesh

BACKGROUND: Rotavirus (RV)–specific immunoglobulin A (IgA) responses following oral RV vaccination are impaired in low-income countries, where the utility of RV-IgA as a correlate of protection (CoP) remains unclear. In a monovalent oral RV vaccine (Rotarix) efficacy trial among infants in Dhaka, Bangladesh, we identified factors associated with poor RV-IgA responses and explored the utility of RV-IgA as a CoP. METHODS: Infants were randomized to receive Rotarix or no Rotarix at 10 and 17 weeks of life and followed with active diarrheal surveillance. RV-IgA concentration, seroconversion, and seropositivity were determined at 18 weeks of life and analyzed for correlation(s) with rotavirus diarrhea (RVD) and for contribution to Rotarix vaccine effect. RESULTS: Among vaccinated infants, overall RV-IgA geometric mean concentration was 21 U/mL; only 27% seroconverted and 32% were seropositive after vaccination. Increased RV-specific maternal antibodies significantly impaired immunogenicity. Seroconversion was associated with reduced risk of RVD through 1 year of life, but RV-IgA seropositivity only explained 7.8% of the vaccine effect demonstrated by the clinical endpoint (RVD). CONCLUSIONS: RV-IgA responses were low among infants in Bangladesh and were significantly impaired by maternal antibodies. RV-IgA is a suboptimal CoP in this setting; an improved CoP for RV in low-income countries is needed. CLINICAL TRIALS REGISTRATION: NCT01375647.