THE IMMUNOGENICITY OF 3 HAEMOPHILUS-INFLUENZAE TYPE-B CONJUGATE VACCINES AFTER A PRIMARY VACCINATION SERIES IN PHILIPPINE INFANTS

Serum antibody responses to three Haemophilus influenzae type b (Hib) capsular polysaccharide-protein conjugate vaccines (PRP-OMP, PRP-T, an d HbOC) were evaluated in 174 Philippine infants after a primary vacci nation series. Children were randomized to receive one of the Hib vacc ines (Hib groups) or into a control group. Vaccination was carried out at six, 10 and 14 weeks of age based on the local Expanded Program of Immunization schedule. Sera were collected at six weeks of age for th e Hib groups and one month after the third dose for all subjects. Anti -Hib concentrations were determined by the Farr-type radioimmunoassay. There were no significant differences (P = 0.3626) in the prevaccinat ion anti-Hib geometric mean concentration (GMC) among the three Hib gr oups. Differences in the GMC after the primary series of three doses w ere significant (P < 0.0001); GMC was highest for PRP-T (6.62 mu g/ml) , followed by HbOC (1.9 mu g/ml), then PRP-OMP (1.06 mu g/ml), and low est for the control group (0.11 mu g/ml). We conclude that all three H ib conjugate vaccines (PRP-T, HbOC, sind PRP-OMP) were immunogenic aft er three primary doses among Philippine infants.