Immunogenicity and reactogenicity of lowered doses of rhesus rotavirus vaccine strain MMU 18006 in young children.

Rhesus rotavirus oral vaccine strain MMU 18006 at a dose of 10(5) plaque-forming units (PFU), a 1:10 dilution of the original undiluted vaccine, is highly immunogenic in young children. Fevers have occurred, however, on Days 3 and 4 following vaccination. This study was conducted to determine whether febrile reactions could be eliminated and immunogenicity maintained by (1) giving smaller doses of vaccine or (2) vaccinating younger infants. Thirty-one children between 3 and 11 months of age received, in a randomized, double blind manner, either 10(4) PFU of vaccine virus, 10(3) PFU of vaccine virus or placebo. All recipients of the 10(4) PFU dose had a seroresponse; however, some degree of immunogenicity was lost with the smaller dose (10(3) PFU). Fevers were observed in recipients of both of the lowered doses of vaccine but the febrile reactions were related to the age of the vaccinee. No infant younger than 5 months of age experienced a temperature elevation, whereas the majority of children older than 5 months had fevers. Our data suggest that the lack of reaction in the younger infants correlates with the presence of prevaccination neutralizing antibody, presumably transplacentally acquired. We conclude that the rhesus rotavirus oral vaccine at a dose of 10(4) PFU is immunogenic and appears to be safe in young infants.