EFFICACY, SAFETY, AND IMMUNOGENICITY OF A MENINGOCOCCAL GROUP-B (15-P1.3) OUTER-MEMBRANE PROTEIN VACCINE IN IQUIQUE, CHILE

A meningococcal group B (15:P1.3) outer membrane protein vaccine was t ested for efficacy in a randomized, double-blind controlled study in I quique, Chile. A total of 40 811 volunteers, ages 1-21 years, enrolled in the study. Volunteers received two doses of vaccine six weeks apar t by jet injector. Both the experimental vaccine and the control vacci ne (Menomune(R), A, C, Y and W135 meningococcal polysaccharide vaccine ) were well tolerated with minor side-effects. Active surveillance for suspected cases of meningococcal disease was conducted for 20 months in Iquique. Eighteen cases of group B meningococcal disease were confi rmed during the 20 months. Efficacy was estimated to be 51% (p=0.11) f or all ages combined. In children aged 1-4 no protection was evident, but in volunteers aged 5-21 vaccine efficacy was 70% (p=0.045). The Ig G antibody response by ELISA was characterized by a large booster effe ct after the second dose, followed by a substantial drop in antibody l evels by 6 months. The youngest children had the highest responses. Th e bactericidal antibody response, on the other hand, was characterized by the lack of a significant booster response, higher responses in th e older children, and an increase in the geometric mean titer in the l ater months of the study in the older children.