Phase I study of the immunogenicity and safety of conjugated Hemophilus influenzae type b vaccines in the elderly.

In infants, vaccines consisting of a carrier protein conjugated to the bacterial capsular polysaccharide (PRP) are far more protective against Hemophilus influenzae type b (Hib) disease than unconjugated PRP. To determine the tolerability and immunogenicity of Hib conjugate vaccines in the elderly, we vaccinated 30 volunteers, aged 69-84 years, with either PRP conjugated to an outer membrane protein complex (PRP-OMP), or PRP oligomers conjugated to CRM197, a nontoxic, mutant diphtheria toxin (HbOC). Prior to vaccination, 40% of subjects had serum anti-PRP antibody levels < 1.0 microgram ml-1. Four weeks following vaccination, all subjects had concentrations > 1.0 microgram ml-1, a level generally considered to be protective. The post-vaccination geometric mean concentrations were 35.5 and 50.1 micrograms ml-1 for the PRP-OMP and HbOC groups, respectively (0.05 < P < 0.10). Subjects in the HbOC group, but not the PRP-OMP group, showed, on average, ten fold increases in IgG antibody to diphtheria toxoid after conjugate vaccination. Side-effects of vaccination were mild except in one subject given HbOC, who developed extensive erythema and swelling of the injected arm.