title: Immunization with Haemophilus influenzae type b polysaccharide vaccine at 18 and 24 months of age: evidence of decreased immunogenicity.
abstract: In order to assess the immunogenicity of a two-dose regimen of Haemophilus influenzae type b polysaccharide vaccine, the immune response to vaccine given at both 18 and 24 months of age was compared to the response to a single dose at 24 months of age. Following immunization at 24 months of age, the geometric mean antibody concentration of children previously immunized at 18 months (0.53 micrograms/ml) was significantly lower than that of children who received a single dose of vaccine at 24 months (1.03 micrograms/ml; p = 0.03). A four-fold rise in antibody concentration was demonstrated in 31% of children who had received two immunizations and 53% of children immunized for the first time at 24 months of age (p = 0.02). These results suggest that the administration of a dose of plain polysaccharide vaccine at 18 months of age blunted the response to reimmunization at 24 months of age. A subgroup of children who failed to respond to one or two doses of plain polysaccharide vaccine were immunized with polysaccharide-diphtheria toxoid conjugate vaccine. The majority of these children developed a significant rise in antibody concentration in response to conjugate vaccine.
authors.affiliation: Department of Pediatrics, Dalhousie University, Halifax, Nova Scotia.
authors.forename: E E
authors.initials: EE
authors.lastname: Adderson
authors.forename: N
authors.initials: N
authors.lastname: Chisholm
authors.forename: S A
authors.initials: SA
authors.lastname: Halperin
mesh_terms: D000367:Age Factors; D000907:Antibodies, Bacterial / Q000096:biosynthesis*; D016667:Bacterial Capsules; D001428:Bacterial Vaccines / Q000008:administration & dosage / Q000276:immunology*; D002675:Child, Preschool; D015331:Cohort Studies; D004168:Diphtheria Toxoid / Q000276:immunology; D018073:Haemophilus Vaccines; D006193:Haemophilus influenzae / Q000276:immunology*; D006801:Humans; D007114:Immunization; D007223:Infant; D011135:Polysaccharides, Bacterial / Q000008:administration & dosage / Q000276:immunology*; D011446:Prospective Studies
chemical_list: D000907:Antibodies, Bacterial; D001428:Bacterial Vaccines; D004168:Diphtheria Toxoid; D018073:Haemophilus Vaccines; C044237:Haemophilus influenzae type b polysaccharide vaccine; C052180:Haemophilus influenzae type b-polysaccharide vaccine-diphtheria toxoid conjugate; D011135:Polysaccharides, Bacterial