title: Differences in the immunogenicity of three Haemophilus influenzae type b conjugate vaccines in infants.
abstract: OBJECTIVE
  To compare the immunogenicity of three Haemophilus influenzae type b (Hib) conjugate vaccines in infants residing in different geographic areas.
  
  
  METHODS
  A multicenter, randomized immunogenicity trial with sera assayed in one laboratory without knowledge of vaccine brand status. In Minneapolis and Dallas, infants were vaccinated at 2, 4, and 6 months of age; in St. Louis, infants were vaccinated at 2 and 4 months of age.
  
  
  METHODS
  A convenience sample of 458 infants recruited largely from private pediatric practices.
  
  
  RESULTS
  At each of the study sites, the respective trends between the anticapsular antibody responses of the infants assigned to the different conjugate vaccine groups were similar. After one or two doses, Hib polysaccharide conjugated to outer membrane protein complex of Neisseria meningitidis (PRP-OMP) was more immunogenic than Hib polysaccharide-tetanus toxoid conjugate (PRP-T), or Hib oligomers conjugated to the mutant diphtheria toxin CRM197 (HbOC) (p less than 0.001). After two doses, PRP-T was more immunogenic than HbOC (p less than or equal to 0.001). After three doses there was no significant difference in the geometric mean antibody concentrations of the three groups, and 88% to 97% of the infants had greater than 1.0 microgram/ml of antibody. The HbOC vaccine elicited a 10-fold lower antibody response after two doses (0.45 micrograms/ml vs 5.9 micrograms/ml) and a threefold lower antibody response after three doses (6.3 micrograms/ml vs 22.9 micrograms/ml) than observed by us previously with a prelicensure lot of this vaccine (p less than 0.001). Because of these low responses, the infants in St. Louis who received two doses of HbOC were revaccinated with unconjugated PRP at a mean age of 8.9 months. This group was immunologically primed, as evidenced by a 10-fold increase in geometric mean antibody concentration after vaccination at an age when unprimed infants do not normally respond to this vaccine.
  
  
  CONCLUSIONS
  In infants in three geographic regions, PRP-OMP elicited earlier acquisition of serum antibody than the other two conjugate vaccines; however, after three doses the antibody concentrations of the three groups were not significantly different. The reason for the markedly lower immunogenicity of HbOC vaccine than reported previously is unknown.
authors.affiliation: Edward Mallinckrodt Department of Pediatrics, Washington University School of Medicine, St. Louis, Missouri.
authors.forename: D M
authors.initials: DM
authors.lastname: Granoff
authors.forename: E L
authors.initials: EL
authors.lastname: Anderson
authors.forename: M T
authors.initials: MT
authors.lastname: Osterholm
authors.forename: S J
authors.initials: SJ
authors.lastname: Holmes
authors.forename: J E
authors.initials: JE
authors.lastname: McHugh
authors.forename: R B
authors.initials: RB
authors.lastname: Belshe
authors.forename: F
authors.initials: F
authors.lastname: Medley
authors.forename: T V
authors.initials: TV
authors.lastname: Murphy
mesh_terms: D000367:Age Factors; D000907:Antibodies, Bacterial / Q000032:analysis*; D001425:Bacterial Outer Membrane Proteins / Q000276:immunology*; D001426:Bacterial Proteins / Q000276:immunology*; D001428:Bacterial Vaccines / Q000276:immunology*; D018073:Haemophilus Vaccines; D006193:Haemophilus influenzae / Q000145:classification / Q000276:immunology*; D006801:Humans; D007115:Immunization Schedule; D007223:Infant; D007231:Infant, Newborn; D008910:Minnesota; D008923:Missouri; D011135:Polysaccharides, Bacterial / Q000276:immunology*; D013745:Tetanus Toxoid / Q000276:immunology*; D013781:Texas; D014611:Vaccination; D014614:Vaccines, Synthetic
chemical_list: D000907:Antibodies, Bacterial; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D001428:Bacterial Vaccines; D018073:Haemophilus Vaccines; C055753:Haemophilus influenza type b polysaccharide vaccine-tetanus toxin conjugate; C061964:Haemophilus influenzae-type b polysaccharide-Neisseria meningitidis outer membrane protein conjugate vaccine; D011135:Polysaccharides, Bacterial; D013745:Tetanus Toxoid; D014614:Vaccines, Synthetic; C061963:HibTITER protein, Haemophilus influenzae