HAEMOPHILUS-INFLUENZAE TYPE B-SPECIFIC ANTIBODY IN INFANTS AFTER MATERNAL IMMUNIZATION

Objective, To study the kinetics of Haemophilus influenzae type b (Hib )-specific antibody in infants born to mothers immunized with an Hib p olysaccharide or one of two Hib conjugate vaccines. Study design, Seru m antibody to the polyribosylribitol (PRP) moiety of Hib was measured by radioimmunoassay and enzyme-linked immunosorbent assay at birth and at 2 and 6 months of age in infants born to women immunized with Hib polysaccharide or conjugate vaccine (PRP-D and HbOC). A subset of infa nts greater than or equal to 6 months of age was immunized with Hib co njugate vaccine after licensure of this vaccine for infants, A compari son group of 18 infants born to unimmunized women received the same Hi b conjugate vaccine on a similar schedule. Results. Total PRP antibody concentrations were 1.50, 14.4 and 20.4 mu g/ml in 2-month-old infant s born to mothers immunized with polysaccharide, PRP-D and HbOC vaccin es, respectively, and 2.54, 1.35 and 2.46 mu g/ml in 6-month old infan ts, Infants born to mothers immunized with polysaccharide vaccine had significantly less PRP antibody at 2 months of age but similar antibod y concentrations at 6 months of age, Persistence or increases in total PRP antibody during 6 months were noted in 21 of 47 (44.6%) study inf ants. A subset of study and comparison infants was immunized with a me an of 2.6 doses of Hib vaccines between 6 months and 2 years of age, a nd all infants had total PRP antibody concentrations greater than or e qual to 0.15 mu g/ml. Conclusion. Conjugate Hib vaccines administered during the last trimester of pregnancy resulted in significantly highe r PRP antibody titers in infants at birth and 2 months of age than did polysaccharide vaccine. A subset of infants born to immunized mothers was subsequently immunized with Hib conjugate vaccine and had antibod y concentrations similar to those in infants born to nonimmunized wome n.