Dose-response study of RIT 4237 oral rotavirus vaccine in breast-fed and formula-fed infants.

The RIT 4237 live attenuated bovine rotavirus vaccine was given orally at three dose levels to 75 breast-fed, 40 formula-fed and 24 fasting infants ages 4 to 6 months. Vaccine of 10(8.3) (50% tissue culture-infective doses) (TCID50) per dose gave a neutralizing antibody response in 14 of 14 (100%) formula-fed, in 18 of 26 (69%) breast-fed and in 5 of 8 (63%) fasting infants, or an overall response rate of 77% (37 of 48). The overall response rate to a vaccine of 10(7.2) TCID50 per dose was 61% (33 of 49), or slightly but not significantly lower than that at the higher dose level. On the other hand a vaccine of 10(6.3) TCID50 per dose gave a significantly (P less than 0.01) lower composite response rate of 33% (14 of 42). The overall serologic response rate to the vaccine at the two higher doses was somewhat better (24 of 28, 86%) in formula-fed infants than in breast-fed infants (37 of 52, 71%). However, the response rate of the breast-fed infants can also be considered satisfactory. Thus the current recommendation for use of the RIT 4237 vaccine would be administration of a dose of at least 10(8) TCID50 after feeding with either formula or breast milk.