Sensitization and reactogenicity of two doses of candidate antileprosy vaccine Mycobacterium w.

M.w vaccine is one of the antileprosy vaccines under test in an ongoing comparative vaccine trial in South India. The objective of the present study was to examine the sensitizing ability, as measured by skin test reactions to Rees' MLSA and lepromin, and reactogenicity of M.w vaccine in the local population. Two doses of M.w, 1 x 10(9) bacilli and 5 x 10(9) bacilli, were used, in two separate studies of 395 and 400 "healthy" individuals aged 1-65 years. In each study, the study subjects received either M.w vaccine or normal saline (control), by random allocation. The results showed that healing of vaccination lesions was uneventful although the healing process was somewhat prolonged with the higher dose. The mean size of lesions was 7.0 mm and 9.5 mm with the low and high doses of the vaccine, respectively. The results also showed that M.w vaccine in a dose of 1 x 10(9) bacilli, failed to induce post-vaccination sensitization as measured by reactions to Rees' MLSA and by Fernandez and Mitsuda reactions to lepromin-A. However, when the dose of the vaccine was increased to 5 x 10(9) bacilli the mean sizes of post-vaccination reactions to Rees' MLSA and lepromin-A (both early and late) were significantly larger in the vaccine group compared to that in the control group. The sensitizing effect attributable to the vaccine was of the order of 1.5 mm to 1.8 mm.