Efficacy of BCG vaccine against leprosy and tuberculosis in northern Malawi.

Protection afforded by BCG (bacillus Calmette-Guérin) vaccines against tuberculosis and leprosy varies widely between different populations. In the only controlled trial which assessed protective efficacy of BCG (Danish and Pasteur strains) against both diseases, there was slightly more protection against leprosy than against tuberculosis. We have studied the protective efficacy of BCG (Glaxo, freeze dried) vaccine against these two diseases in Karonga District, northern Malawi. BCG vaccination was introduced into this population in 1974. Prior information about BCG scar status was available for 83,455 individuals followed up between 1979 and 1989. 414 new cases of leprosy and 180 new cases of tuberculosis were found in this population over that period. Protection was estimated at 50% or greater against leprosy, and there was no evidence for lower protection against multibacillary (84%; 95% confidence interval 26% to 97%) than against paucibacillary (51%; 30% to 66%) disease. There was no statistically significant protection by BCG against tuberculosis in this population. These findings add to the evidence that BCG vaccines afford greater protection against leprosy than against tuberculosis.