Effects of ICRC antileprosy vaccine in healthy subjects.

Long-term effects of the administration of the ICRC antileprosy vaccine in healthy subjects have been investigated both in household contacts of leprosy patients and noncontacts in a general population. Each volunteer received a dose of vaccine containing either 0.5 x 10(9) or 1.7 x 10(7) bacilli intradermally. The vaccine induces a dose-dependent lepromin conversion in negative subjects at 8 weeks after vaccination. One year later, the conversion rates are more than 90% in both high- and low-dose groups. Lepromin conversion is stable for at least 3 years. When administered to the lepromin-positive contacts, the vaccine induces a statistically significant increase in intensity of the reaction at 6 months. During the 3-year observation period, the subjects have remained healthy and no untoward effects, including any neurological lesions, have been observed. There has also been no change in the circulating level of antibodies against the phenolic glycolipid-I antigen of Mycobacterium leprae as a result of vaccination. The vaccine thus induces not only stable immunity but is safe and, being given as a single injection, has a high acceptability. Its field trials will begin soon.