MIP vaccine in leprosy: A scoping review and future horizons

Mycobacterium Indicus Pranii (MIP) vaccine is a killed vaccine developed in India for leprosy with immunotherapeutic as well as immunoprophylactic effects. MIP, earlier known as Mycobacterium welchii, is a rapidly growing non-pathogenic mycobacterium. The novelty of this bacterium is due to its translational application as an immunotherapeutic agent. When administered intradermally, the vaccine induces cell-mediated immunity in the host towards Mycobacterium leprae. It leads to faster clinical and histopathological improvement, rapid bacillary clearance, and also lepromin conversion in anergic leprosy patients. The beneficial role of the MIP vaccine in augmenting the therapeutic efficacy of Multidrug Therapy (MDT), particularly in highly bacillated leprosy patients, is well documented in various studies from India. The role of the vaccine in reactional states is controversial, with varied results in different studies. Overall, it is found to decrease the frequency of type 2 lepra reactions and is useful in recalcitrant erythema nodosum leprosum. Even though there may be an increased likelihood of type 1 reactions, no additional nerve function impairment is attributed to the vaccine in various studies. In household contacts of leprosy who are administered MIP, it is noted to confer protection from disease lasting up to 10 years. It may prove to be a cost-effective strategy in national leprosy programmes. Apart from local injection site reactions, the vaccine is relatively safe, but it is not recommended in pregnancy and lactation. This article provides an overview of the MIP vaccine's clinical application in the context of leprosy spanning over 40 years. It also considers the vaccine's possible future applications in the management of disease-related complications and achieving the long-term goal of zero leprosy.