The study was carried out within the area covered by the Bandim Health Project in Bissau, the capital of Guinea Bissau, West Africa. The study area, within the suburbs of Bissau, has a population of approximately 70,000 who are under demographic surveillance. Routine infant immunisations are given at 3 health centers in the area; babies who deliver in the national hospital are given BCG before they leave. Overall coverage with BCG is high (> 95%).