The Karonga Prevention Trial - Which BCG?

Abstract

A leprosy vaccine trial, the Karonga Prevention Trial, was started in Karonga District in Northern Malawi in January 1986. The objectives are essentially: to test whether BCG + killed M. leprae gives greater protection against leprosy than BCG alone and to test whether a repeat BCG vaccination can add to the protection against clinical leprosy given by the first BCG vaccination. The results of these studies, undertaken in late 1985 and in 1986, are the subject of this presentation. In contrast with our conversion rates the protective immunity observed after vaccination with Glaxo BCG in the Malawi population is long term and at least 50%. This confirms again that delayed type hypersensitivity reactions and protective immunity are largely if not entirely unrelated phenomena and that conversion rates are of poor predictive value for the amount of protective immunity likely to be observed. Since we have no data on the protective immunity of Copenhagen BCG in this population we can however not be sure whether post vaccination ulcer sizes are of similarly poor predictive value.