South Indian leprosy vaccine trial: important lessons for mycobacterial immunology

171,400 individuals living in Chingleput District, South India, were recruited into a major leprosy vaccine trial organized by the Indian Council for Medical Research. The participants were randomized to receive a placebo, a plain BCG vaccine, a combination of BCG plus killed leprosy bacilli, or else a killed environmental mycobacterial vaccine: either 'Mycobacterium W', or 'Mycobacterium ICRC'. Eighty-five percent of these individuals were examined for leprosy between August 1993 and February 1995 and 75% were examined between January 1997 and September 1998. The codes were broken in December 1998, and revealed that each of the vaccines had provided significant protection over the interval between 4 and 8 years after vaccination: 65 .5% for the ICRC bacillus, 64% for combined BCG and killed My cobacterium leprae, 34% for BCG alone and 257% for the W bacillus. l These figures, and the data behind them, include several findings of considerable importance for research on mycobacterial immunology and vaccines.