COMPARATIVE-EVALUATION OF REACTOGENICITY AND IMMUNOGENICITY OF 2 DOSAGES OF ORAL TETRAVALENT RHESUS ROTAVIRUS VACCINE

Objective. To compare the safety and immunogenicity of two dosages of tetravalent rhesus rotavirus vaccine (RRV-TV) and the effect of age at dosing. Methods. A total of 195 infants were stratified by age into 2 groups, 6 to 12 weeks and 16 to 24 weeks, and randomly assigned to re ceive a single dose of placebo or RRV-TV containing either 4 x 10(5) o r 4 x 10(6) plaque-forming units (pfu). Symptoms were recorded for 5 d ays after vaccination. Anti-rotavirus IgA and neutralizing antibody to human rotavirus serotypes G1 to G4 and RRV were measured in serum obt ained pre- and post-vaccination. Results. Rates of fever >38 degrees C (9%), diarrhea (6%) and vomiting (8%) were similar in all groups. IgA (69% vs. 49%, P = 0.02) and RRV (85% vs. 66%, P = 0.004) seroconversi on rates were significantly higher in the 4 x 10(6) pfu vaccine group as were antibody titers to RRV (440.2 vs. 263.7, P = 0.04). Older infa nts demonstrated significantly higher seroconversion rates and antibod y titers for IgA (71% vs. 52%, P = 0.03; and 110.6 vs, 54.8, P = 0.004 ) and RRV (92% vs. 66%, P = 0.05 and 498.3 vs. 205.6, P = 0.01) at eit her dose level than did the younger infants. There were no significant differences in seroconversion rates or antibody titers to human rotav irus types G1 to G4 between the two vaccination groups. Conclusions. R RV-TV at a dose of 4 x 10(6) pfu can be safely administered to infants 6 to 24 weeks of age. A single dose of 4 x 10(6) pfu of RRV-TV was si gnificantly more immunogenic than a single dose of 4 x 10(5) pfu but d id not improve responses to the human serotypes. Older vaccine recipie nts demonstrated significantly higher IgA and neutralizing antibody se roconversion rates and antibody titers than younger infants independen t of dosage.