Background: In view of high mortality and morbidity from Haemophilus influenzae type b (Hib) in young Papua New Guinean children, the incorporation of a Hib conjugate vaccine into a nationwide immunization program would be of major public health benefit. The choice of the Hib conjugate vaccine will be based on the evaluation of several Hib conjugate vaccines, after consideration of such factors as the ease of incorporation into the current vaccination schedule, cost, kinetics of antibody responses and safety.
Methods: This study evaluated the safety and immunogenicity of Hib polysaccharide-Neisseria meningitidis outer membrane protein complex conjugate vaccine (PRP-OMPC) in Papua New Guinea. 95 children were recruited at Goroka Base Hospital, Eastern Highlands Province, and enrolled in the study. PRP-OMPC was administered at ages 2, 4 and 12 to 15 months. Blood was collected before each dose, one month after the second and booster doses, and at ages 18 and 24 months. Antibody to PRP (anti-PRP) was measured by radioimmunoassay.
Results: PRP-OMPC was generally well tolerated. At successive sampling times from the prevaccination bleed through the 1-month post-booster bleed, geometric mean titres were 0.18, 1.45, 2.54, 1.03 and 8.05 micrograms/ml, respectively (n = 60). The proportions of subjects with anti-PRP titres > or = 1.0 microgram/ml were 2%, 62%, 73%, 47% and 93%, respectively (n = 60). Persistence of anti-PRP was ascertained in 41 subjects. The GMTs at 18 and 24 months were 3.42 and 2.0 micrograms/ml, respectively.
Conclusions: PRP-OMPC was found to be immunogenic after the first dose and to elicit a robust booster response. Antibody titres persisted until age 24 months, at which time 100% of subjects had anti-PRP > or = 0.15 microgram/ml. These results are consistent with previous studies in US Native American infants and in Gambian infants.