This study is designed to evaluate the safety of the TB vaccine MVA85A in healthy children and infants in South Africa. A single vaccination with MVA85A has been shown to be safe and highly immunogenic in a wide range of subjects in previous clinical trials. In this trial,we will vaccinate 24 children with 5 x 10^7pfu of MVA85A and three groups of 36 infants with 2.5 x 10^7, 5 x 10^7 or 1 x 10^8 pfu.