In a four cell trial, a single 10(4) plaque-forming unit dose of rhesus 
rotavirus (RRV) vaccine (serotype G3), a human rotavirus-rhesus rotavirus 
reassortant vaccine with serotype G1 specificity, a similar vaccine with 
serotype G2 specificity, or a placebo was administered with buffer orally at 2 
months of age to 800 Peruvian infants. Only the RRV vaccine was associated with 
a febrile response (< 38 degrees C) that occurred in 9% of the infants on day 4 
after vaccination. Diarrhea or other side-effects were not associated with 
administration of vaccine. Vaccine strains were shed by only 12-18% of the 
infants as determined by examination of a single stool specimen obtained on days 
4 or 5 after vaccination. Fifty per cent of vaccines developed an IgA ELISA 
seroresponse; however, a serotype-specific seroresponse by plaque reduction 
neutralization was demonstrated in < 20% of the participants against each of the 
three candidate vaccine strains. Vaccine efficacy was evaluated by twice-weekly 
home surveillance for diarrheal diseases during 24 months post-immunization. 
Rotavirus diarrheal episodes were identified by ELISA. Only the RRV vaccine had 
a significant protective efficacy (29%, p = 0.03, chi-square test) against 
rotavirus diarrhea. Analysis of vaccine efficacy against rotavirus episodes of 
any severity in which no other enteropathogen was isolated showed a trend 
towards higher vaccine efficacy. In addition, a similar trend was observed in 
rotavirus-only episodes in which there was some degree of dehydration or when 
health services were utilized. Serotype G1 or G2 rotavirus strains were most 
prevalent during surveillance. Neither serotype G1 or serotype G2 vaccines were 
protective against serotype 1 or 2 rotavirus diarrhea, respectively. The 
serotype G2 vaccine was 84% protective against serotype 1 and 2 dehydrating 
rotavirus diarrhea in the small numbers of individuals evaluated. We conclude 
that one dose of 10(4) p.f.u. of the RRV, serotype G1, or serotype G2 rotavirus 
vaccine failed to induce either an adequate serotype-specific seroresponse or 
serotype-specific protection in children immunized at 2 months of age. Only the 
RRV vaccine induced a low level of protection against rotavirus diarrhea mainly 
of serotype G1 specificity. Future studies need to explore whether higher 
vaccine dose and/or more than one dose would increase the immunogenicity and 
efficacy of the rotavirus vaccine, especially in developing countries with a 
high level of baseline rotavirus antibodies.