Overview
- Meningococcal disease is caused by the Gram-negative bacterium Neisseria meningitidis (the meningococcus). It remains a significant public health issue globally, causing both endemic and epidemic disease in developed and developing countries.
- Approximately 10% of humans harmlessly carry N. meningitidis in the oronasopharynx. On rare occasions, the bacteria may cross the epithelium and enter the bloodstream, causing a sudden onset of sepsis and/or meningitis with high complication and fatality rates, even with appropriate antibiotic treatment.
- A limited number of strains cause the majority of invasive disease. In healthy individuals, these almost always express a protective polysaccharide capsule on their cell surface.
- There are 12 capsular serogroups, of which A, B, C, W, X, and Y cause the vast majority of invasive meningococcal disease worldwide.
- Polysaccharide-based vaccines target the capsule and are therefore serogroup-specific.
- Plain (unconjugated) polysaccharide vaccines were first developed and used to control serogroup A epidemics in sub-Saharan Africa and serogroup C disease among military and college populations. However, they have limitations such as poor immunogenicity in young children, hyporesponsiveness with repeat doses, lack of immune memory, and no effect on carriage.
- Conjugated polysaccharide vaccines overcome these limitations and significantly reduce carriage. Large-scale vaccination of cohorts with high carriage (catch-up campaigns) is highly effective in inducing herd protection.
- Serogroup C conjugate vaccines have been highly successful in dramatically reducing disease in countries that implemented immunization programs along with catch-up campaigns.
- Meningococcal quadrivalent conjugate vaccines are now being introduced into vaccination schedules.
- With the introduction of a meningococcal serogroup A conjugate vaccine, serogroup A disease has virtually disappeared from sub-Saharan countries that implemented these campaigns.
- The serogroup B polysaccharide is poorly immunogenic; therefore, broad-coverage protein-based serogroup B vaccines have been developed.
