W135 strain of the disease
The emergence of Neisseria meningitidis W135
Meningococcal disease is caused by the meningococcus ( Neisseria meningitidis) and is the only form of bacterial meningitis to cause epidemics. Twelve serogroups are currently recognized; serogroups A, B and C are responsible for the vast majority of cases. Historically the epidemics in African meningitis belt have been primarily caused by Neisseria meningitidis serogroup A.
For several decades, N. meningitidis W135 has been known to have been associated with clinical cases, including epidemics, which have always been on a very small scale. Two outbreaks coinciding with pilgrimage seasons for Hajj/Umra in 2000 and 2001 have been associated with N.meningitidis W135. A number of cases with identical etiology were reported in several countries in Asia, Europe and in the United States; an epidemiological link with international travel to Saudi Arabia, during which close contact with returning pilgrims could be established, was also reported. In addition, the WHO Collaborating Centre for Meningococcal Disease in Marseille (France) has isolated N. meningitidis W135 in samples from different African countries, such as Algeria, Cameroon, the Central African Republic, Senegal and Chad. The circulation of this serogroup among returning pilgrims has also been found in carriage studies in Morocco, Sudan and Oman in 2000.
In 2002, the first large-scale epidemic occurred in Burkina Faso with 13 000 cases reported, of whom 1400 died.
Implications for public health
The emergence of N. meningitidis W135 as the agent responsible for a large-scale epidemic has public health implications. WHO expert consultations were held (Geneva, September 2001, Ouagadougou, September 2002) on the changing epidemiology of meningocccal disease, with particular reference to the emergence of N.meningitidis W135. The need to rationalize use of available global stocks of vaccine and to adapt epidemic response strategies to epidemiological profiles are challenges for the immediate future. WHO is currently strengthening laboratory and epidemiological surveillance systems in the countries of the African meningitis belt to detect and characterize the serogroups responsible for epidemics to guide its response effectively; assure supplies of effective drugs and ability of health care systems to deliver these to the affected populations; protect the population at risk through mass immunization, if the vaccine is available.
A better vaccine
It is probable that production capacity of vaccines targeting the serogroup W135 will remain insufficient for the next epidemic seasons. WHO is working with manufacturers to make available an effective vaccine against the circulating strains, including N.meningitidis W135 at an affordable price for countries most at risk.
In addition, the current polysaccharide vaccine has some drawbacks for vaccination campaigns in sub-Saharan Africa: it does not provide long-lasting protection, hence the need for repeated vaccination of at least 80% of the population each time an epidemic occurs; logistic demands and costs are very high; the vaccine has no effect on colonization or transmission of the organism within populations, so travelers returning from an epidemic zone can transmit the infection to close contacts.
In 2001, the Meningitis Vaccine Project, with financial support from the Bill and Melinda Gates Foundation was established by WHO and the Program for Appropriate Technology in Health (PATH). The goal of this 10-year partnership is to develop and introduce a conjugate meningococcal vaccine as a tool for eliminating epidemic meningitis as public health problem in sub-Saharan Africa.