Postpartum immunization with rubella virus vaccine and antibody response in breast-feeding infants.

Women who were susceptible to rubella, whether they had elected to breast-feed or formula-feed their infants, received immunization with subcutaneously administered rubella antibody 27/3 live, attenuated rubella virus vaccine in the postpartum period. The breast-fed or formula-fed infants of these mothers who had been immunized subsequently received active immunization with the rubella antibody 27/3 vaccine at 15 to 18 months of age. A second group of naturally immune women who were seropositive for rubella did not receive immunization after childbirth. However, infants of naturally immune mothers who did not receive immunization received immunization with the rubella vaccine and served as controls. Seroconversion for rubella antibody developed in over 94% of susceptible women who were seronegative for rubella after postpartum immunization. The infants of these mothers had no rubella antibody activity in the cord blood; however, 13% of such infants exhibited rubella antibody in serum at 6 months of age. On the other hand, 44% of breast-fed infants of naturally immune mothers (controls) demonstrated rubella antibody activity at 6 months of age. Subsequent immunization with rubella vaccine in breast-fed infants whose mothers had received postpartum immunization resulted in a serum antibody response that was similar to the response observed in the formula-fed infants or the infants of naturally immune mothers who had not received immunization. These data suggest that early neonatal exposure to the rubella virus in breast milk does not enhance or suppress subsequent responses to current programs of rubella vaccination in early childhood.