Protection of BCG against the Paucibacillary and Multibacillary clinical forms
As per many findings, BCG protects from Paucibacillary and Multibacillary leprosy. There is also a hypothesis that BCG could shift the cases from a multibacillary to paucibacillary end of leprosy gamut by making a shift within the entire cell-mediated immune response and this raises the risk for milder & transient types of leprosy while protecting from more severe forms like multibacillary ones.
Hence, the fall in the stats of paucibacillary cases because of BCG vaccination may be masked by a change in multibacillary-paucibacillary shift. There isn’t a statistical proof for supporting the hypothesis even if there exists a suggestion of a low BCG protection for paucibacillary leprosy compared to multibacillary leprosy.
There exists lack of strength because of fewer studies which offer separate estimates for multibacillary and paucibacillary forms & these have some wide confidence intervals also. While comparing the statistics of patients that were vaccinated with BCG among paucibacillary and multibacillary cases, remarkable differences have been identified with lower frequency of BCG vaccination among multibacillary patients as compared to paucibacillary patients. This, hence, seems to support the hypothesis of multibacillary-paucibacillary leprosy shift because of BCG vaccination, however, further studies shall be done for its verification.
Place of BCG in strategy to control leprosy
Numerous studies have concluded that there exists very strong proof of BCG protection from leprosy in the general population & this protection may be even more in populations that are at greater risk of leprosy like household contacts. But that protection may vary in diverse settings & are not known completely. BCG protection fades with time, however; the duration of protective impact seems to be adequate. BCG is broadly used in the endemic nations for protection of children from severe TB disease. Although not explicitly mentioned, the role of it in controlling leprosy is recognized. Indeed, there exists a common misconception that there isn’t a vaccine against leprosy. Leprosy continues to prevail despite BCG vaccination, could be perfectly elucidated by the inconsistency of its protection in many settings because of the previous infection with EM & the fading of protection due to age combined with the vaccination being given most during infancy. If there exists a high leprosy rate in endemic regions with BCG vaccination, that rate would probably be still greater in regions with no vaccination. Also, several results support the maintenance of a good BCG coverage in the high-burden nations.