Bacterial meningitis remains a serious threat to global health, accounting for an estimated annual 170 000 deaths worldwide.
Three species, Haemophilus influenzae, Streptococcus pneumoniae and Neisseria meningitidis, are responsible for most cases of bacterial meningitis occurring beyond the neonatal period. Since the introduction of H. influenzae type b (Hib) conjugate vaccines, N. meningitidis and S. pneumoniae have become the commonest causes of bacterial meningitis in the world. With the progressive implementation of the conjugated polysaccharide vaccines against pneumococcus, it is likely that N. meningitidis will remain a major agent of meningitis worldwide.
Moreover, N meningitidis is the only bacteria able to generate epidemics of meningitis.
Meningococcus serogroups that are responsible for severe meningitis belong to only 6 groups: Nm A, B, C, X, Y and W135.
Group A meningococci are characterized by their propensity to cause large scale epidemics in developing countries, specifically in the countries of the African 'meningitis belt'.
Group B meningococcus (Nm B) is the most important cause of endemic meningitis in industrialized countries, accounting for 30% to 40% of the cases in North America and for up to 80% in some European countries.NmB also can cause severe, persistent epidemics, which begin slowly but may persist for 10 years or longer, as seen in the past in Norway; in Cuba, Brazil and areas of Chile; and currently in New Zealand. Vaccines against groups A, C, Y and W135 include bivalent or plurivalent polysaccharide (PS) and conjugate vaccines, some of which have already been combined with routinely administered vaccines to fit within the EPI regimen. Thus, the introduction of the NmC conjugate vaccines as an addition to routine infant immunization in the UK has had a tremendous impact on the incidence of the disease, resulting in a more than 90% decrease in the number of deaths and clinical cases and a 66% decrease in asymptomatic carriage.
Because epidemic group A meningococcal meningitis continues to be a major problem in countries of the sub-Saharan meningitis belt, the Meningitis Vaccine Project (MVP), a partnership between the WHO and PATH, has developed a NmA conjugate vaccine. The vaccine has successfully been tested in Phase I, II and II/III clinical trials in India and African countries of the meningitis belt: Mali, The Gambia and Senegal. In December 2009, the vaccine was licensed in India for vaccination of individuals 1-29 years old and prequalified by WHO in June 2010. At the end of 2010, around 20 million population from Burkina Faso, Mali, and Niger were immunized with the vaccine and these countries reported the lowest number of confirmed meningitis A cases ever recorded during the 2011 epidemic season. At the end of 2011, Cameroon, Chad and Nigeria have vaccinated more than 22 million individuals. Continuing surveillance for cases of meningitis and monitoring of vaccination coverage will be crucial to confirm the effects of the vaccine as it is introduced across the meningitis belt.
Group B N. meningitidis, is the only serogroup against which capsular PS vaccines cannot be developed, due to antigenic mimicry with PS in human neurologic tissues. Efforts to find novel vaccine antigens to protect against serogroup B disease have identified several sub-capsular proteins, including factor H binding protein, Neisserial adhesin A, and Neisseria-heparin binding antigen. As the proteins used in these vaccines can also be found across all meningococcal serogroups, such vaccines have the potential to protect against both serogroup B and additional serogroups. Among the several candidate vaccines that are currently under investigation in clinical trials, the vaccine known as 4CMenB has induced, in a pivotal phase IIb study, robust immune response when given alone or with other routine vaccines. Although preliminary data are promising, the role these vaccines could play in controlling meningococcal disease remains to be determined.
Last updated: February 2012