Leprosy vaccines – A voyage unfinished

Leprosy, a chronic granulomatous disease caused by Mycobacterium leprae, is endemic in many regions of the world. With introduction of multidrug therapy in 1982, there has been a dramatic reduction in the prevalence of leprosy, but new cases continue to appear. There have been more than 200,000 new cases per year for the past 10 years. There is a renewed interest in leprosy vaccines with immunoprophylactic and immunotherapeutic roles. Due to the difficulty in cultivating M. leprae in artificial media, vaccine strategies have centered on the use of cross-sensitizing mycobacteria. Bacillus Calmette–Guerin (BCG) has been the most popular among these, but with a widely varying protective efficacy reported from different parts of the world. In three meta-analyses, BCG has shown strong evidence of efficacy against leprosy. Recently, India has focused interest on another vaccine, Mycobacterium indicus pranii vaccine earlier known as Mycobacterium w. To overcome the limitations of these whole cell vaccines, various recombinant BCGs and subunit vaccines have been developed and studied in experimental models. These often yield inconsistent results. However, a new subunit recombinant vaccine – LepVax holds promise and has completed Phase 1a clinical trials successfully.