Objective. - To evaluate maternal responses to Haemophilus infiuenzae type b (Hib) polysaccharide-tetanus protein conjugate vaccine (polyribosylribitol phosphate-tetanus or PRP-T) given to pregnant Gambian women, the transplacental transfer of antibody, and the effect of maternal immunization on infant responses to the vaccine. Design. - An open, randomized immunogenicity study. Setting. - A busy urban health center in The Gambia. Study participants. - A total of 451 pregnant women enrolled during the third trimester of pregnancy. Intervention. - Study participants were randomized to three groups. In one group, mothers were given PRP-T during the third trimester and their infants were given PRP-T at 2, 3, and 4 months of age. In the second group, mothers received PRP-T and infants were given inactivated poliovirus vaccine. In the third group, mothers received meningococcal A and C vaccine, and their infants received PRP-T. Main Outcome Measures. - Anti-PRP antibody measurements of maternal, cord, and infant blood. Results. - Vaccinated women had a marked increase in total anti-PRP antibody (geometric mean titer, 9.0 μg/mL), which was greatest in women in their first or second pregnancy. Previous tetanus vaccination during the same pregnancy and high concentrations of antitetanus antibody were associated with lower anti-PRP responses. In infants of PRP-T recipients, cord blood anti-PRP IgG concentrations were 61% of simultaneous maternal concentrations. In vaccinated infants of vaccinated mothers, geometric mean anti-PRP antibody concentrations at birth, 2 months of age, and 5 months of age were 1.92, 0.35, and 2.84 μg/mL, respectively, while in vaccinated infants of unvaccinated mothers, the corresponding concentrations were 0.29, 0.12, and 3.91 μg/mL. At 2 months of age, 60% of infants of vaccinated mothers and 26% of infants of unvaccinated mothers had anti-PRP antibody concentrations considered to be protective (>0.15 μg/mL). Conclusions. - In areas where much invasive Hib disease occurs in infants younger than 6 months, maternal immunization may help to reduce the risk of Hib disease in infants too young for immunization.
