AN 8-YEAR FIELD TRIAL ON ANTILEPROSY VACCINES AMONG HIGH-RISK HOUSEHOLD CONTACTS IN THE CALCUTTA METROPOLIS

One-hundred-seventy-nine lepromin-negative household contacts were vac cinated with heat-killed Mycobacterium leprae, BCG, or a combination o f the two. Vaccination induced lepromin positivity in 131 of these con tacts. Over an 8-year follow-up period, 12 lepromin-positive contacts developed leprosy, all tuberculoid; while 2 lepromin-negative vaccinat ed contacts developed leprosy, both lepromatous. Overall, 7.8% of the vaccinated contacts developed the disease. Seven-hundred-fourteen hous ehold contacts were not vaccinated, and served as controls. Among the 504 who were lepromin positive, leprosy developed in 35, all tuberculo id, over the 8-year follow up. Among the 210 lepromin-negative unvacci nated contacts, 61 developed leprosy: tuberculoid in 29, borderline in 4, lepromatous in 8, and indeterminate in 20. Overall, 13.5% of the 7 14 unvaccinated contacts and 29.0% of the 210 unvaccinated, lepromin-n egative contacts developed leprosy. Vaccination could not induce lepro min positivity in al contacts. The three vaccines were equally effecti ve in inducing lepromin positivity. Vaccination reduced the overall in cidence of leprosy from 13.5% to 7.8% among household contacts but did not reduce the incidence of lepromatous leprosy (1.2% of all the vacc inated and 1.1% of all the unvaccinated contacts).