Bacterial Meningitis
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, MenAfriVac®. 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. Serum Institute of India (SII) has received a marketing authorization for export and use of MenAfriVacTM in Africa as single-dose mass vaccination campaigns in 1-29 year olds in the 25 countries of the African belt, a target population of about 250 million people. MenAfriVacTM received WHO prequalification on 23 June 2010 and progressive introduction will be rolled out starting with the 3 hyperendemic countries (Burkina Faso, Mali, Niger) in West Africa in 2010-11.
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. Consequently, vaccine research against Nm B has focused on outer membrane proteins. Vaccines developed in Norway, Cuba or The Netherlands are being used to fight the Nm B epidemics in these countries. However, truly successful development of a broad specificity NmB vaccine is expected to come from a "reverse vaccinology" approach, or 'genome mining'.
Last updated: August 2010
