Leprosy in Malawi. 2. Background, design and prospects of the Karonga Prevention Trial, a leprosy vaccine trial in northern Malawi.

The Karonga Prevention Trial is the largest vaccine trial ever mounted in Africa. It is designed to test two hypotheses: (i) whether the addition of killed Mycobacterium leprae can increase the protection against leprosy (and tuberculosis) imparted by BCG alone; and (ii) whether repeating a BCG vaccination can increase upon the protection provided by an initial dose. The rationale and design of the trial are discussed in relation to the history of vaccination against leprosy and to several contending arguments which determined the ultimate protocol. The potential of the trial to reveal statistically significant differences between the vaccines being compared is discussed, as are the implications of possible results for future research and control of leprosy.