Thus, BCG prophylaxis study in South India, provided the unique results of importance in several ways.
(1) BCG (0.1 mg) gave about 25% Protective efficacy which is not relevant from the public health point of view for protection against leprosy.
(2) Smear positive leprosy was not prevented.
(3) BCG efficacy was best seen in the youngest age-group but substantially weaned over a period of 15 years.
(4) Prior sensitization to M.tuberculosis or environmental mycobacteria as judged by PPD-S and PPD-B skin tests did not affect much the efficacy of BCG.
Subsequent to the availability of large quantity of M. leprae through Armadillo the next generation on vaccine studies became possible. Three large studies have been conducted using BCG + Killed M.leprae as one of the arms in these studies. Results are already available for the study from Venezuela and Malawi. It is claimed that in both these countries BCG gave substantial level of protection against leprosy. These observations did' not emerge from prospectively controlled trials of BCG, but with the starting point of persons having BCG scar and those who were not having BCG scar. It was also observed in both these studies that addition of M.leprae to BCG was not of much help in enhancing the efficacy of BCG in protection against leprosy. Results from the study from India are expected shortly.
In addition to some of these prospective studies, case control studies using BCG scar as the evidence for vaccination, have also been conducted. It is well known that BCG scar may disappear to a substantial extent particularly in infants. Another possibility that is to be considered is the "take" for BCG and subsequent resultant scar might be indicative of protection against leprosy, as was seen in the past lepromin conversion studies results from Myanmar. Therefore, even though the results from case control studies demonstrate substantial protection against leprosy, at least for some clinical forms, these studies are not comparable and not as much reliable as the prospective cohort studies.
With the M. leprae genome project nearing its completion, and M. Tb genome project nearly completed, the prospects for new generation of leprosy vaccines have brightened. There is a growing need for collaboration and interdependence between TB and leprosy immunology research. In the face of these developments, several new questions emerge. It is generally felt that leprosy is already declining all over the world. Do we need a leprosy vaccine at all at this stage? It is interesting to note that even though leprosy prevalence is coming down substantially, new case detection in countries where MDT programmes are implemented, did not show parallel decline. It is certain that various countries will not be able to maintain vertical leprosy programmes with substantial expenditure indefinitely. Therefore, there will be growing need and demand for integrated health services with a resultant danger of dilution of the programme. As of now, there are no indications of resurgence of leprosy and we hope that such kind of danger may not be there. However, an effective leprosy vaccine maybe needed in certain countries at least in certain areas in the near future.
