Varicella vaccination is recommended for all susceptible women of childbearing age. However, vaccination during pregnancy can result in congenital varicella syndrome, characterized by neurologic and eye defects, limb hypoplasia, and muscle atrophy. Ideally, a susceptible woman identified during pregnancy should be vaccinated immediately postpartum. Concerns exist that the virus could be transmitted in breast milk and cause possible adverse events in the infant. Bohlke and colleagues studied the secretion of varicella virus into breast milk following maternal vaccination and sought any evidence of vaccine exposure in breastfed infants of vaccinated mothers.

The authors studied a group of patients from a large health maintenance organization with approximately 2,100 births per year. Prenatal screening for immunity to varicella began in this group in 1999.Varicella-seronegative women identified by prenatal screening were eligible for the study if they were at least 18 years of age, had no contraindications to vaccination, agreed to be vaccinated after counseling, and intended to breastfeed for at least one month following delivery. The immune status of each patient and her child was confirmed before enrollment in the study.

Twelve women participated in the study. Before immunization, each patient and her child were confirmed to have no recent exposure to varicella, live vaccines, or blood products. Patients received their first vaccine dose at least six weeks postpartum and their second dose after another four weeks. Each woman collected samples of breast milk on the mornings of days 3, 5, 7, 9, 11, 13, 15, 17, 19, and 21 after each dose of vaccine. These samples were tested by polymerase chain reaction (PCR) capable of detecting virus and distinguishing between wild and vaccine-associated varicella. Serum was collected one month after each vaccination to test for IgG, and blood was obtained from all infants one month after the second maternal vaccination for similar testing. Blood also was obtained from six infants for PCR evidence of varicella. The women were asked to report any rashes occurring in themselves or their children.

Nine of the 12 women were white, and five were younger than 30 years. Only three had previously given birth. All 12 women seroconverted after the first vaccination. No varicella virus was detected in the 217 breast-milk samples, and no infants developed IgG antibodies or PCR evidence of virus transmission. One woman developed a rash that was negative for varicella DNA after vaccination. No rashes were reported in the infants.

The authors conclude that no evidence was found of varicella virus excretion in breast milk or of other transmission of virus to infants when mothers were vaccinated post-partum. They encourage physicians to identify susceptible women during pregnancy and ensure postpartum vaccination.