**Core Concept**
BCG (Bacillus Calmette-Guérin) vaccine is a live, attenuated vaccine used primarily to protect against severe forms of tuberculosis (TB), particularly in countries with high TB prevalence. It works by stimulating a cell-mediated immune response, which helps to control the growth of Mycobacterium tuberculosis.

**Why the Correct Answer is Right**
The BCG vaccine is administered via intradermal injection, which allows for the localized immune response to develop in the skin. This response involves the activation of antigen-presenting cells, such as dendritic cells, which then stimulate T-cells to differentiate into effector and memory T-cells. The vaccine's efficacy is greatest in areas with high TB prevalence, where the risk of exposure to M. tuberculosis is high.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because BCG vaccine is not primarily used to protect against latent TB infection.
**Option B:** This option is incorrect because BCG vaccine is not given orally.
**Option C:** This option is incorrect because BCG vaccine's primary mechanism of action is not through the production of antibodies.

**Clinical Pearl / High-Yield Fact**
In countries with low TB prevalence, the BCG vaccine may actually increase the risk of severe forms of TB, such as disseminated TB, in infants and young children. This is because the vaccine's efficacy wanes over time, and the risk of exposure to M. tuberculosis may be low.

**Correct Answer:** D.