Investigators:

KHRC: Seth Owusu-Agyei, Kwaku-Poku Asante

NHRC: Abraham Hodgson, Rita Baiden, Elizabeth Awini

LSHTM: Daniel Chandramohan, Brian Greenwood

Epidemics of cerebrospinal meningitis (CSM) have occurred every five to ten years in the meningitis belt of sub-Saharan Africa through out the twentieth century. In 1996, an epidemic in this region caused over 300,000 cases and many thousands of deaths. The CSM epidemics in sub-Saharan Africa are usually caused by meningococci belonging to serogroup A. However, in 2002 a major outbreak in Burkina Faso was caused by meningococci belonging to serogroup W135 and this is a major cause for concern.

Vaccination with group A + group C meningococcal polysaccharide vaccines has been undertaken in countries of the African meningitis belt since the 1970s Mass vaccination in response to an emerging epidemic has been shown to prevent cases but has had little impact on the frequency of epidemics. This is partly due to the fact that polysaccharide vaccines induce only short lasting immunity, are not very effective in young children and have little or no effect on nasopharyngeal carriage. These together with the threat of epidemics caused by serogroup W135 still remains a major cause for concern.

A quadrivalent A,C,Y,W-135 vaccine which consists of 50 µg each of the respective purified bacterial capsular polysaccharides has been shown to be safe and to induce a four fold increase in bactericidal antibody titre in 100% of initially seronegative 3-13 year-old children.7 The quadrivalent A,C,Y,W-135 vaccine has been shown to be safe and immunogenic in infants but the antibody levels decreased rapidly. Although the quadrivalent vaccine could be used to control serogroup W135 epidemics, this vaccine is not used in sub-Saharan Africa because it is relatively expensive. The quadrivalent vaccine is primarily used to protect pilgrims to the annual Hajj in Mecca, Saudi Arabia who are legally required to receive this vaccine before undertaking the pilgrimage.

A new trivalent polysaccharide vaccine (Mencevax™ ACW, GSK) was licensed in January 2003 and produced in limited quantities for use in the control of W135 disease in the African meningitis belt. The safety and immunogenicity of this vaccine is unlikely to be inferior to the quadrivalent vaccine as the antibody responses to each of the four polysaccharides in the quadrivalent vaccine are serogroup-specific and independent. The trivalent ACW135 vaccine was licensed by Belgian Regulatory Authorities based on the historical safety, immunogenicity and clinical efficacy data of the quadrivalent ACYW135 vaccine and a requirement for a posteriori impact evaluation (including immunogenicity and safety data) of the trivalent vaccine . Thus, data on safety and immunogenicity of the new ACW135 polysaccharide vaccine are needed urgently for an evaluation of its continued use in the control of serogroup W135 epidemics in sub Saharan Africa.

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