The protective effectiveness of natural rotavirus infection in an American Indian population.

The degree of protection conferred by natural rotavirus infection was estimated through analyses of data gathered as part of a 2-year rotavirus vaccine study of 1185 Native American infants. In 292 placebo recipients with complete serum sample sets, rotavirus IgA antibody indicative of infection before 2 months of age was associated with a 58% decrease in symptomatic infections throughout the trial. In all 391 placebo recipients, the preventive effectiveness of an initial symptomatic infection was 72% overall and 94% within 6 months following the infection. In contrast to studies conducted at other sites in the United States, serotype G3 was the predominant serotype associated with gastrointestinal episodes (80%). The effectiveness of an initial serotype G3 episode with respect to preventing subsequent serotype G3 episodes was 91%.