**Core Concept**
BCG (Bacillus Calmette-Guérin) vaccine is a live attenuated vaccine used for the immunoprophylaxis of tuberculosis and leprosy. The vaccine works by inducing a cell-mediated immune response against the Mycobacterium tuberculosis and Mycobacterium leprae antigens.

**Why the Correct Answer is Right**
BCG vaccine has been shown to provide partial protection against leprosy, particularly in high-prevalence areas. The vaccine stimulates the production of cytokines such as interferon-gamma, which helps to activate macrophages and kill the M. leprae bacteria. This immune response is crucial in preventing the development of leprosy in individuals who have been vaccinated.

**Why Each Wrong Option is Incorrect**
**Option B:** MMR (Measles, Mumps, and Rubella) vaccine is a live attenuated vaccine that protects against measles, mumps, and rubella viruses, but it does not provide any protection against leprosy.
**Option C:** ICRC bacillus is not a recognized vaccine or bacterium related to immunoprophylaxis of leprosy.
**Option D:** Anthrax vaccine is used to protect against Bacillus anthracis, a different bacterium that causes anthrax disease.

**Clinical Pearl / High-Yield Fact**
BCG vaccine is not 100% effective in preventing leprosy, and its effectiveness can vary depending on the region and population. However, it remains an important tool in controlling leprosy outbreaks and reducing the incidence of the disease in high-risk areas.

**Correct Answer:** **✓ Correct Answer: A. BCG**