Meningococcal meningitis and septicaemia are caused by various serogroups of Neisseria meningitidis. Endemic disease occurs worldwide and is mostly caused by meningococci of serogroups A, B, or C, although group Y is gaining importance, at least in parts of the United States. The group A meningococcus is the predominant cause of large epidemics. Particularly in the so-called African meningitis belt, major group A epidemics occurring at intervals of 7-14 years result in excessive morbidity and mortality among children and young adults. In recent years, group W135 meningococci have also caused outbreaks in this region as well as in Saudi Arabia, whereas several western countries have experienced outbreaks of group C strains.
Meningococcal disease is associated with high case-fatality rates (5%-15%) even where adequate medical services are available. Chemoprophylactic measures are in general insufficient for the control of this disease.
Immunity following meningococcal infection is sero-group-specific. Current internationally marketed meningococcal vaccines are based either on combinations of group-specific capsular polysaccharides (A and C, or A, C, Y and W135) or on a conjugate between group C, specific polysaccharidge and a protein carrier. The polysaccharidge vaccines are safe and highly immunogenic, although the group C component is ineffective in children under 2 years of age. On the other hand, the recently introduced serogroup C conjugate vaccine is safe and efficacious even in the youngest children. Monovalent polysaccharide vaccines are not readily available, and so far no group A conjugate vaccine has reached the market. Vaccines against group B meningococci have shown only modest efficacy in both children and adults.