PROTECTIVE EFFICACY AGAINST SEROTYPE-1 ROTAVIRUS DIARRHEA BY LIVE ORAL RHESUS-HUMAN REASSORTANT ROTAVIRUS VACCINES WITH HUMAN ROTAVIRUS VP7 SEROTYPE-1 OR SEROTYPE-2 SPECIFICITY

Rhesus-human rotavirus (RV) reassortant vaccine strains D x RRV or DS 1 x RRV with VP7 serotype 1 or 2 specificity were evaluated for safety, immunogenicity and protective efficacy in a double blind placebo-controlled three cell trial involving 359 infants ages 2 to 5 months. The titer of the D x RRV vaccine was 10(4) and that of the DS 1 x RRV vaccine was 10(5) plaque-forming units/1-ml dose. The vaccines were acceptably reactogenic, each inducing a transient febrile response in fewer than one-third of the vaccinees. Seroconversion by RV enzyme-linked immunosorbent assay IgA antibody was detected in 61 and 75% of the vaccinees receiving a single dose of the serotype 1 or 2 reassortant vaccine, respectively. Efficacy against RV diarrhea was evaluated in two successive epidemic seasons; RV serotype 1 was prevalent in both. Clinical efficacy was observed with both vaccines and was associated with seroconversion after vaccination; considering only such vaccinees both vaccines showed equal efficacy. The overall rates of protection for the two vaccines combined against clinical RV disease in children with seroconversion after vaccination were 92 and 59% in the first and second RV epidemic seasons, respectively. Protection against asymptomatic RV infection, as measured by serologic responses, was 59% in the first season and nil in the second season. It is concluded that each of the reassortant RV vaccines was effective in inducing protection against symptomatic RV disease associated with RV serotype 1.