Abstract
The pattern of epidemic meningococcal disease in the African meningitis belt may be influenced by the background level of population immunity but this has been measured infrequently. A standardised enzyme-linked immunosorbent assay (ELISA) for measuring meningococcal serogroup A IgG antibodies was established at five centres within the meningitis belt. Antibody concentrations were then measured in 3930 individuals stratified by age and residence from six countries. Seroprevalence by age was used in a catalytic model to determine the force of infection. Meningococcal serogroup A IgG antibody concentrations were high in each country but showed heterogeneity across the meningitis belt. The geometric mean concentration (GMC) was highest in Ghana (9.09 μg/mL [95% CI 8.29, 9.97]) and lowest in Ethiopia (1.43 μg/mL [95% CI 1.31, 1.57]) on the margins of the belt. The force of infection was lowest in Ethiopia (λ = 0.028). Variables associated with a concentration above the putative protective level of 2 μg/mL were age, urban residence and a history of recent vaccination with a meningococcal vaccine. Prior to vaccination with the serogroup A meningococcal conjugate vaccine, meningococcal serogroup A IgG antibody concentrations were high across the African meningitis belt and yet the region remained susceptible to epidemics.
Highlights
Epidemics of meningococcal disease have occurred at irregular intervals across the Sahelian and sub-Sahelian regions of Africa, the African meningitis belt, for over 100 years.[1]
We have undertaken a study of community levels of serogroup-specific IgG antibody to N. meningitidis serogroup A (NmA) in six countries in the African meningitis belt before the introduction of the serogroup A conjugate vaccine, MenAfriVacTM, to investigate heterogeneity in the level of exposure across the meningitis belt and to use age specific antibody titres to measure the force of infection.[13]
Final results obtained in Ghana are shown as an example in S1 Fig. Following the validation exercise, quality control of the results obtained on analysis of the cross-sectional survey samples was ensured by monitoring the key parameters of the standard curve as well as the local positive controls, as shown for Ethiopia in S2A Fig
Summary
Epidemics of meningococcal disease have occurred at irregular intervals across the Sahelian and sub-Sahelian regions of Africa, the African meningitis belt, for over 100 years.[1]. It is known that protective immunity to Neisseria meningitidis can be induced by meningococcal carriage,[2] infection with other non-pathogenic Neisseria species, such as N. lactamica[3]and possibly by other bacteria.[4,5] There is some evidence that background immunity may be impaired with infection by other bacteria that induce blocking antibodies.[6] The immune response to meningococcal polysaccharide and conjugate vaccines has been studied in the African meningitis belt[7,8,9,10] on several occasions but there have been few studies of population levels of antibody to N. meningitidis in the African meningitis belt.[11,12] we have undertaken a study of community levels of serogroup-specific IgG antibody to N. meningitidis serogroup A (NmA) in six countries in the African meningitis belt before the introduction of the serogroup A conjugate vaccine, MenAfriVacTM, to investigate heterogeneity in the level of exposure across the meningitis belt and to use age specific antibody titres to measure the force of infection.[13] To ensure that patterns of antibody could be compared across sites, we implemented standardised methods supported by careful quality control
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