ANTIBODY-RESPONSE OF NAVAJO CHILDREN PRIMED WITH PRP-OMP VACCINE TO BOOSTER DOSES OF PRP-OMP VS HBOC VACCINE

We compared in 12- to 15-month-old American Indian infants the safety and immunogenicity of two licensed Haemophilus influenzae type b (Hib) conjugate vaccines, PRP-OMP (PedvaxHib(R)) and HbOC (HibTITER(R)), ad ministered as booster vaccinations. All infants previously received PR P-OMP for their primary Hib vaccinations at 2 and 4 months of age. The geometric mean Hib antibody concentrations (mug/ml) measured by radio active antigen-binding assay for those receiving PRP-OMP (n = 17) or H bOC (n = 18) were 0.593 and 0.449, respectively, before boosting (P no t significant) and 7.46 and 29.5 mug/ml, respectively, after boosting (P < 0.05). PRP-OMP recipients also had lower geometric mean IgG anti- Hib antibody concentrations than HbOC recipients (7.21 vs 28 mug/ml, P = 0.003) and lower bactericidal titers (3.18 vs. 15.4, not significan t). We conclude that HbOC vaccine produced a significantly greater boo ster response than PRP-OMP vaccine when given at 12 to 15 months of ag e to children primed with two doses of PRP-OMP vaccine at 2 and 4 mont hs of age.