Maternal immunization with Haemophilus influenzae type b vaccines in different populations.

Haemophilus influenzae type b (Hib) vaccines provide an excellent model for maternal immunization because effective vaccines are readily available and the vaccines are safe and reliable, and markers of efficacy have been established and standardized. Studies of polysaccharide and conjugate Hib vaccines administered to pregnant women and women of childbearing ages are reviewed in this paper. The type of vaccine has been shown to be important in increasing transplacental passage of maternal antibody. The timing of vaccine during pregnancy is also important in the transfer of this antibody. The total amount of IgG antibody in the mother, as well as the isotype class and subclass of IgG antibody, influences the final levels of antibody in the neonate. Placental integrity has been shown to be important in the active transport of antibody from mother to fetus. The impact of increased levels of Hib antibody in infants at the time of primary immunization with Hib does not appear to interfere with vaccine efficacy, although higher antibody levels in infants at the time of immunization may result in lower total antibody levels following all doses of vaccine. Principles observed in these studies have potential application against other important neonatal pathogens.