Safety and immunogenicity of three doses of a Neisseria meningitidis A + C diphtheria conjugate vaccine in infants from Niger

Background. High rates of endemic disease and recurrent epidemics of serogroup A and C meningococcal meningitis continue to occur in sub-Saharan Africa. A meningococcal A + C polysaccharide diphtheria-toxoid-conjugated vaccine may address this issue. Methods. In Niger three doses of a bivalent meningococcal A + C diphtheria-toxoid-conjugated vaccine (MenD), containing 1, 4 or 16 μg of each polysaccharide per dose, administered at 6, 10 and 14 weeks of age, were compared with Haemophilus influenzae type b-tetanus toxoid-conjugated (PRP-T) vaccine given with the same schedule or with a meningococcal A + C polysaccharide vaccine (MenPS) given at 10 and 14 weeks of age. One blood sample was taken at the time of enrollment (6 weeks of age) and another was taken 4 weeks after the primary series. Results. All doses of MenD were well-tolerated. After the primary series a higher proportion of infants had detectable serum bactericidal activity against serogroup A for each dose of MenD (from 94% to 100%) than for MenPS (31%) or H. influenzae type b-tetanus toxoid-conjugated vaccine (18.9%); P ≤ 0.05. Significant differences were also observed for serogroup C Mend 4 μg or MenD 16 μg (100%) vs. MenPS (69.7%) or Haemophilus influenzae type b-tetanus toxoid- conjugated vaccine (24.3%); P ≤ 0.05. When MenPS vaccine was given to 11- month-old children, the immune response measured by both enzyme-linked immunosorbent assay and serum bactericidal assay was greater in those previously immunized with Mend than in those immunized with MenPS vaccine. Conclusion. MenD was safe among infants in Niger, and immunization led to significantly greater functional antibody activity than with MenPS. The 4-μg dose of MenD for both the A and C serogroups has been selected for further studies.