Comparative immunogenicity of four Haemophilus influenzae type b conjugate vaccines in Alaska Native infants

We compared the immunogenicity of the four available Haemophilus influenzae type b (Hib) conjugate vaccines in Alaska Native infants. Three of the vaccines, Hib oligosaccharide-CRM197 (HbOC), polyribosylribitol phosphate-diphtheria toxoid (PRP-D) and polyribosylribitol phosphate-tetanus toxoid (PRP-T), were given at 2, 4 and 6 months of age, and the PRP Neisseria meningitidis outer membrane protein (PRP-OMP) conjugate vaccine was given at 2 and 4 months of age. Enrollment was largely sequential by vaccine availability beginning with HbOC and ending with PRP-T. A total of 225 infants completed the full vaccination series. Groups of infants receiving the different vaccines did not differ significantly by sex, ethnicity, degree Alaska Native or age at vaccination. The only vaccine that induced a response with the first 2-month dose was PRP-OMP; 91% of infants had > or = 0.15 micrograms/ml and 57% had > or = 1.0 microgram/ml of anti-PRP antibody by 4 months of age. After two doses it also remained the most immunogenic. After the full three vaccine series, trials that requires cough of 21 days is excessively restrictive.