Neisseria meningitidis, the meningococcus is an important cause of meningitis and septicaemia, especially in infants and young adults. Meningococci are divided into serogroups based on the immunochemistry of capsular polysaccharides coating the bacterial cell surface. Five serogroups (A, B, C, W and Y) account for most of the disease. Vaccines consisting of capsular polysaccharide offer protection against serogroups A, C, W and Y but are poorly immunogenic in infants. These vaccines have been improved by chemically conjugating the polysaccharide to carrier protein. These so-called conjugate vaccines are immunogenic in infants, elicit good immunological memory and have been shown to provide good herd immunity by reducing meningococcal carriage. Monovalent serogroup C conjugates are widely used in national immunisation programmes. NIBSC carries out batch release testing of meningococcal conjugate vaccines for Europe and a number of other countries.

The serogroup B polysaccharide is poorly immunogenic and has therefore not been developed as a vaccine. Vaccines based on protein antigens are being developed by several manufacturers. These vaccine candidates offer the prospect of comprehensive protection against all meningococcal disease including that caused by bacteria with the serogroup B capsule.