This study will recruit 30 healthy babies who would not routinely be offered the BCG vaccine in the UK within the first week of life. Babies will be assigned at random to one of three groups of ten babies each. BCG will be given to one group of babies around birth, one at three months old and the last group will not get BCG during the study. Babies will stay in the study until 13 months old and have five blood tests over this period.