Blood samples were collected from around 800 participants in each country during the first cross-sectional survey in 2010 and from individuals recruited to the household contact studies. Each of the African centres has received training in ELISA techniques so that they can determine the group-A specific IgG concentrations in their serum samples. Mali and Niger are also using a Serum Bactericidal Antibody (SBA) to determine the prevalence of bactericidal antibodies in these samples. The serology studies are supported by the HPA Vaccine Evaluation Unit, Manchester. This work will allow us to describe the patterns of natural immunity against Men A across the meningitis belt and to determine the level of antibody that protects against carriage acquisition.