Differential protective effect of bacillus Calmette-Guerin vaccine against multibacillary and paucibacillary leprosy in Nagpur, India.

For this paper we conducted a secondary data analysis to test the hypothesis that a linear trend exists in the protective effect of bacillus Calmette-Guerin (BCG) vaccine against types of leprosy. We used data from two previous case-control studies to perform an unmatched test for linear trend. We observed that both the studies revealed a significant linear trend (P<0.00001). One study that estimated an insignificant protective effect of BCG against paucibacillary leprosy showed a significant departure from linearity. We conclude that, the protective effect of BCG vaccination is differential across severity of leprosy as it brings about a shift in the immune response to a higher level of cell mediated immunity. We recommend that future studies dealing with the protective effect of BCG against leprosy should also conduct an analysis for trend.