Antibody-mediated intracellular neutralization as a correlate of risk for rotavirus gastroenteritis in vaccinated infants 2256577

Abstract Introduction Rotavirus vaccines are highly effective in high-income countries at reducing severe gastroenteritis, but show poor efficacy in low- and middle-income regions. The reasons for this discrepancy remain unclear, creating an urgent need for improved vaccines and reliable correlates of protection. Traditional serum IgA ELISAs and neutralization assays do not fully capture the breadth of antibody-mediated immunity to rotavirus. Mounting evidence suggests that antibodies targeting the internal capsid protein VP6 may mediate an additional intracellular layer of protection following viral entry, a mechanism not routinely assessed in vaccine evaluation. Methods We have developed a novel intracellular neutralization assay to measure antibody activity against internal rotavirus proteins exposed only after viral entry. Our assay was validated and optimized for human serum samples collected from infants enrolled in a phase III rotavirus vaccine trial. We evaluated intracellular neutralization as a correlate of risk for gastroenteritis in infants receiving the standard live-attenuated vaccine (Rotarix) compared to a candidate non-replicating rotavirus vaccine (NRRV). Results Infants vaccinated with Rotarix had a significantly higher intracellular neutralization response post-vaccination than those receiving NRRV. This finding contrasted with conventional neutralization assays, in which NRRV appeared superior. Importantly, Rotarix provided greater protection against clinical disease. Among Rotarix-vaccinated infants, intracellular neutralization was significantly boosted by vaccination in controls but not in those who developed gastroenteritis. Conclusion This intracellular neutralization assay captures a previously unmeasured component of antibody-mediated protection against rotavirus. We have demonstrated its value as a correlate of risk for rotavirus gastroenteritis in vaccinated human infants, and future work will evaluate its wider role as a correlate of protection. Funding Source PATH, Wellcome Trust Topic Categories Vaccines and Immunotherapy (VAC)