Effectiveness of Bacillus Calmette Guerin (BCG) vaccination in the prevention of leprosy: a population-based case–control study in Yavatmal District, India

Abstract

Objective. To estimate the effectiveness of Bacillus Calmette Guerin (BCG) vaccination in the prevention of leprosy. Study design. Population-based case–control study. Methods. The study was carried out in Yavatmal District, Maharashtra, India. It included 364 cases of leprosy (diagnosed by the World Health Organization's criteria), born since 1962, that were detected during a leprosy survey conducted by the Government of Maharashtra in 2,175,514 people. Each case was pair-matched with one neighbourhood control for age, sex and socio-economic status. Exclusion criteria for controls included past or current history of tuberculosis or leprosy. BCG vaccination status was assessed by examination for the presence of a BCG scar, immunization records if available and information from subjects/parents of children. Subjects who were uncertain about BCG vaccination were not included. Results. A significant protective association between BCG and leprosy was observed [odds ratio=0.46, 95% confidence intervals (CI) 0.34–0.61]. Overall vaccine effective--ness (VE) was 54% (95% CI 39–66). BCG effectiveness against multibacillary, paucibacillary and single skin lesion leprosy was 68% (95% CI 26–86), 57% (95% CI 29–74) and 48% (95% CI 22–65), respectively. Analysis of linear trend revealed a significant linear association between the protective effect of BCG and the type of leprosy. The BCG vaccine was more effective in those aged ≤20 years compared with those aged >20 years (VE 61%, 95% CI), among females compared with males (VE 60%, 95% CI), in lower socio-economic strata compared with upper and middle strata (VE 57%, 95% CI), and in subjects who had a BCG scar size ≤5 mm compared with those with a BCG scar size >5 mm (VE 61%, 95% CI). However, these differences were not statistically significant, as reflected by the overlapping 95% CIs. The overall prevented fraction was 35% (95% CI 22–46). Conclusion. The current study identified a beneficial role of BCG vaccination in the prevention of leprosy in the study population.