Antipolyribosyl Ribitol Phosphate Response of Premature Infants to Primary and Booster Vaccination With a Combined Diphtheria-Tetanus-Acellular Pertussis-Hepatitis B-Inactivated Polio Virus/Haemophilus influenzae Type b Vaccine

Abstract

BACKGROUND. Prematurity may be a risk factor for Haemophilus influenzae type b vaccine failure. This article evaluates the Haemophilus influenzae type b immunogenicity of a hexavalent diphtheria-tetanus-acellular pertussis-hepatitis B-inactivated poliovirus/Haemophilus influenzae type b vaccine in preterm infants (<37 weeks' gestation). METHODS. This was an open-label, parallel group study. Preterm (N = 94) and term infants (N = 92) received 3 doses of a diphtheria-tetanus-acellular pertussis-hepatitis B-inactivated poliovirus/Haemophilus influenzae type b vaccine at 2, 4, and 6 months with a booster dose at 18 to 20 months. Antipolyribosyl ribitol phosphate antibody concentrations were determined in serum samples taken before and 1 month after primary and booster vaccination. RESULTS. Postprimary seroprotection rates (antipolyribosyl ribitol phosphate ≥0.15 μg/mL) were lower in preterm than in term infants (92.5% vs 97.8%), with antipolyribosyl ribitol phosphate geometric mean concentrations of 2.241 vs 4.247 μg/mL. A progressive reduction in immune response to the Haemophilus influenzae type b antigen was observed with decreasing length of gestation and decreasing birth weight when cutoff ≥1 μg/mL was considered. Prebooster seroprotection rates and antipolyribosyl ribitol phosphate geometric mean concentrations were low in both groups (antipolyribosyl ribitol phosphate ≥1.0 μg/mL in 10.7% of preterm and 28.4% of term infants). A vigorous response to booster vaccination was seen in both groups, with no differences in postbooster seroprotection rates or antipolyribosyl ribitol phosphate geometric mean concentrations between the 2 groups (antipolyribosyl ribitol phosphate ≥1.0 μg/mL in 100% of preterm and 98.5% of term infants). CONCLUSIONS. Primary vaccination with a hexavalent diphtheria-tetanus-acellular pertussis-hepatitis B-inactivated poliovirus/Haemophilus influenzae type b vaccine at 2, 4, and 6 months with a booster dose at 18 to 20 months elicits a satisfactory antipolyribosyl ribitol phosphate response in preterm infants compared with term controls. Immunologic response decreased with decreased gestational age and birth weight.