Effect of maternal antibodies on the infant immune response.

Transplacentally-acquired antibodies are important for protection of infants in the early months of life. Maternal antibodies may dampen the infant's primary antibody response to infection or immunization. Even without a measurable response to the initial antigen exposure, the infant will usually have evidence of priming at the time of repeat exposure. No evidence for the development of fetal tolerance after immunization during pregnancy has occurred subsequently in infants following active vaccination.