 Volunteers in this study will receive BCG vaccination at the standard dose of 2-8x105 cfu. BCG SSI containing Mycobacterium bovis strain Danish 1331 is preferred as it is licensed in the UK for vaccination. However BCG SSI can frequently go into short supply globally with impact on UK supply. In the event of this occurring, BCG vaccine supplied by the Sii Serum institute of India will be used instead which contains Mycobacterium bovis BCG strain Moscow 361 I and is on the WHO list of prequalified vaccines. The same strain will be used for all volunteers. 