The incidence rates of acquisition and loss of serogroup A meningococci will be investigated in the household contacts of serogroup A carriers detected during the initial cross-sectional surveys and, in countries where vaccination is undertaken, after vaccination.

Once a serogroup A carrier has been detected, all household contacts (expected to be in the range of 10–20) will be swabbed fortnightly for two months, and then monthly for a further four months. This study will allow rates of acquisition and loss of carriage to be determined. A blood sample will be collected at the time that the initial swabs are collected for measurement of meningococcal antibodies. These measurements will allow the titre of bactericidal antibody that provides protection against serogroup A meningococcal carriage to be determined.