Maternal Immunization With Haemophilus Influenzae Type b Polysaccharide-Tetanus Protein Conjugate Vaccine in the Gambia

Abstract

Objective. —To evaluate maternal responses to Haemophilus influenzae 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.