Leprosy Vaccine Used Internationally
Different populations with different genetic backgrounds may explain why certain countries have and have not found success in the BCG vaccine against leprosy. Two recent studies in India (54% effectiveness, Zopdey) and Brazil (74% with neonatal vaccination, Cunha ) provide clear evidence that BCG protects against leprosy. Brazilian investigators argue that their results show the importance of neonatal vaccination and that environmental mycobacteria may not affect vaccine efficacy, at least in the Amazon region of Brazil.
Three relatively recent vaccine trials have studied the efficacy of combining the BCG vaccine with killed M.leprae. The main reason for testing this combination is to figure out whether M.leprae-specific antigens are able to improve the efficacy of BCG against leprosy. The first of these three studies was conducted in Venezuela and concluded that the protective efficacy of BCG was proportional to the number of doses (i.e. the number of scars from BCG vaccination) and that protection against leprosy was not necessarily improved with the BCG and M.lepae combination. In a trial done in Malawi, no improvements were seen as well. However, scar-positive individuals showed a further protection against leprosy with a second BCG vaccination.
A trial in southern India showed no positive effect for vaccinating BCG scar-positive individuals, but enhanced protection was shown in individuals who received BCG plus heat-killed M.leprae. They also showed enhanced protection with vaccines that contained Mycobacterium w or ICRC (cultivable leprosy derived mycobacteria probably belonging to M. avium intracellulare complex). ICRC alone and BCG plus heat-killed M.leprae gave approximately the same level of protection (64% (Kartikeyan) and 65% (Gormus), respectively) showing that a killed mycobacterial vaccine containing M.leprae cross-reactive antigens is as effective as a live, attenuated BCG vaccine. But these results are specific to this population and setting. Thus, the controversy still continues over what elements of a leprosy vaccine are superior, though it is generally accepted that the positive effects of vaccination to reduce leprosy are confirmed.
When will we see a universally approved vaccine?
Dr. Tom Gillis of the National Hansen’s Disease Programs says that it is safe to say that in the next five years, there will be one to two new vaccines for tuberculosis that might include a leprosy component. As far as a vaccine exclusively for leprosy, we might see one in the next 5-10 years, then it would take 5-10 years to follow up on it and test it. His estimate is that it could be about 10-20 years before we see an official leprosy vaccine that is universally accepted worldwide.