During pre-vaccination surveys conducted in 2010, pharyngeal swabs were collected from 4,300 and 5,000 age stratified subjects in Mali and Niger respectively. Molecular analysis performed in Oxford, confirmed that there was no serogroup A meningococci among the 48 and 338 isolates of putative meningococci identified in Mali and Niger respectively. In contrast, serogroup A meningococcal carriers were identified in Chad during the course of a related epidemiological study (REF.5699). In addition, during the 2011 African meningitis season, more than 90% of cases of serogroup A meningococcal disease recorded in the meningitis belt came from Chad or Cameroun with very few cases being reported from Mali or Niger. These observations indicate that it may be possible to measure the impact of MenAfriVac™ on serogroup A meningococcal in Chad rather than in Mali or Niger as had been proposed originally.