Transplacental antibody transfer following maternal immunization with polysaccharide and conjugate Haemophilus influenzae type b vaccines.

Passive transfer of antibody to infants born to women immunized during the third trimester of pregnancy with a Haemophilus influenzae type b (Hib) vaccine (PRP polysaccharide or Hib conjugates PRP-D or HbOC) was studied in 50 mothers and infants and 47 nonimmunized mother-infant pairs. Geometric mean total PRP antibody by RIA was 1.2 micrograms/mL at delivery in unimmunized women and 21, 149, and 171 micrograms/mL in women who received PRP, PRP-D, and HbOC, respectively. Mean cord PRP antibody levels were 0.29, 3.0, 17.5, and 29.3 micrograms/mL for the corresponding groups. Postimmunization and cord PRP antibody levels were higher after maternal immunization with conjugate vaccines than with PRP vaccine (P < .01). PRP IgG1 subclass was transmitted more efficiently than IgG2 (56% vs. 35%, P < .01). The proportion of anti-PRP IgG transmitted from immunized mothers to infants correlated with time between immunization and delivery. Administration of PRP conjugate vaccines to women during pregnancy resulted in higher levels of PRP antibodies in infants than did polysaccharide or no vaccine.