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This paper reviews the origin, use, protective efficacy and public health impact of BCG vaccines. The problem of evaluating their efficacy is discussed with reference to various hypotheses which have been proposed to explain the divergent estimates obtained in studies carried out in different areas of the world. It is concluded that, despite the apparent variation in protective efficacy, the extensive use of BCG vaccines (more than three billion doses worldwide in four decades) means that they have had a substantial impact on tuberculosis and leprosy. The problem of explaining BCG's varying protection remains unsolved but of great importance, because of the scale of BCG use and current effort to develop improved vaccines against tuberculosis and leprosy.
Paul Fine (Fri,) studied this question.