VACCINATION OF THAI INFANTS WITH RHESUS-HUMAN REASSORTANT TETRAVALENTORAL ROTAVIRUS VACCINE

In a randomized double blind placebo-controlled study, the rhesus-huma n reassortant tettravalent oral rotavirus vaccine (dose 4 x 10(4) plaq ue-forming units) was evaluated in Thai infants immunized at ages 2, 4 and 6 months. To investigate dose responses and to compare vaccine-in duced and naturally acquired rotavirus immunity in the study populatio n blood specimens were collected before and 1 month after each vaccina tion and at 12 months of age. No adverse reactions attributable to the vaccine were detected in the vaccinees. Sixty-three of 94 (67%) vacci ne recipients showed a seroconversion in rotavirus IgA enzyme-linked i mmunosorbent assay antibodies after one or more doses, whereas only 15 of 93 (16%) placebo-vaccinated control children showed an IgA enzyme- linked immunosorbent assay antibody response, suggestive of natural ro tavirus infection, between 2 and 7 months of age. By measuring rhesus rotavirus-neutralizing antibodies a seroconversion was detected in 49% of the vaccinees and 14% of the controls between 2 and 7 months of ag e. The geometric mean titers of neutralizing antibodies to human rotav irus serotypes 1, 2, 3 and 4 after the completion of vaccinations and at 12 months of age were higher in the vaccinees than in the controls. It is concluded that, even though maternally acquired rotavirus antib odies are commonly present, the rhesus-human reassortant tetravalent v accine is immunogenic in many Thai infants ages 2 to 6 months. The imm unogenicity of this vaccine is enhanced by multiple doses.