<qa>  How many patients per group will be sampled for expression analysis?All contacts will undergo clinical evaluation at enrolment and review. The development of active TB will trigger withdrawal and full treatment. Fortnightly clinical review of group B during the deferred phase will be undertaken. ELISPOT analysis will be performed on all subjects at 0, 1, 4, 13, 26 and 40 weeks in groups A and C, and at 0, 13, 14, 17, 26, 40 and 54 weeks in groups B and D. A subset of 10 patients per group will be sampled for expression analysis at 0, 4, 26 and 40 weeks groups A and C and at 0, 13, 17 and 40 weeks in groups B and D 160 hybridizations in total. 