Which of the following statements is true about BCG vaccination –
**Core Concept**
BCG (Bacillus Calmette-Guérin) vaccination is a live attenuated vaccine used primarily against tuberculosis (TB). The vaccine induces a cell-mediated immune response, particularly involving T lymphocytes, to protect against severe forms of TB, such as TB meningitis and miliary TB, in children.
**Why the Correct Answer is Right**
The correct statement is likely related to the mechanism of action of BCG vaccination. BCG vaccine works by stimulating the immune system to produce a strong response against the TB bacteria. This response involves the activation of T lymphocytes, particularly CD4+ T cells, which recognize and eliminate infected cells. The vaccine also induces the production of cytokines, such as interferon-gamma, which help to activate macrophages and kill the bacteria.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is likely incorrect because BCG vaccination does not provide long-term protection against pulmonary TB in adults. The vaccine's effectiveness wanes over time, leaving adults vulnerable to TB infection.
**Option B:** This option is likely incorrect because BCG vaccination is not a live attenuated vaccine against influenza. The vaccine is specific to TB and does not protect against other infectious diseases.
**Option C:** This option is likely incorrect because BCG vaccination is not a killed-virus vaccine. Live attenuated vaccines, such as BCG, contain a weakened form of the virus or bacteria, whereas killed-virus vaccines contain an inactivated form of the pathogen.
**Clinical Pearl / High-Yield Fact**
BCG vaccination is most effective in preventing severe forms of TB, such as TB meningitis and miliary TB, in children. However, its effectiveness in preventing pulmonary TB in adults is limited, and booster doses may be required to maintain immunity.
**Correct Answer:** C.