Meningococcal vaccine evolution.

Neisseria meningitidis is a leading cause of bacterial sepsis and meningitis worldwide. Invasive meningococcal disease (IMD) can develop rapidly and is associated with high mortality and morbidity. Case fatality in developed countries averages 10% and higher rates are reported in less prosperous regions. The incidence of invasive disease due to Neisseria meningitidis is highly variable according to geographical area and serogroup distribution. The major disease burden is in developing countries; in industrialized countries meningococcal disease occurs sporadically and most IMD is caused by serogroups B and C. In the US serogroup Y is a major cause of meningococcal disease, accounting for more than one third of cases. Polysaccharide vaccines against serogroups A, C, W-135, and Y were developed but they were not so effective in protecting infants, who are at particularly high risk from invasive meningococcal infections. Conjugation of bacterial capsular polysaccharide to a carrier protein generates a T cell dependent immune response and immunological memory from infancy. After the introduction of serogroup C meningococcal conjugate vaccines since 1999, the incidence of serogroup C disease fell dramatically in countries in which they have been used. The first quadrivalent meningococcal conjugate vaccine (MenACWY-D) was licensed in the US in 2005. More recently, another tetravalent meningococcal conjugate vaccine (MenACWY-CRM, Menveo) was licensed in Europe and the US. Although polysaccharide and glycoconjugate vaccines have been developed for serogroups A, C, Y and W-135, currently there are no broadly effective vaccines available for the prevention of meningococcal B disease.