COMPARATIVE IMMUNOGENICITY OF 4 HAEMOPHILUS-INFLUENZAE TYPE-B CONJUGATE VACCINES IN ALASKA NATIVE INFANTS

We compared the immunogenicity of the four available Haemophilus influ enzae 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 th e PRP Neisseria meningitidis outer membrane protein (PRP-OMP) conjugat e vaccine was given at 2 and 4 months of age. Enrollment was largely s equential by vaccine availability beginning with HbOC and ending with PRP-T, A total of 225 infants completed the full vaccination series. G roups of infants receiving the different vaccines did not differ signi ficantly 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 greater-than-or-equal-to 0.15 mug/ml and 57% had greater-than-or-equal-to 1.0 mug/ml of anti-PRP antibody b y 4 months of age. After two doses it also remained the most immunogen ic. After the full three vaccine series, HbOC produced the highest con centrations of antibody; 94% of infants had greater-than-or-equal-to 1 .0 mug/ml. PRP-T had approximately 75% of infants above this antibody concentration, and PRP-D had only 45% of infants with this level. Simi lar-rates of antibody decay were observed for all vaccine groups betwe en 7 and 15 to 18 months of age and duration of antibody was primarily determined by peak antibody achieved. Differences in the pattern and degree of antibody response to each Hib conjugate vaccine were substan tial.