## Core Concept
Live vaccines contain a weakened or attenuated form of a pathogen, which causes a mild or asymptomatic infection, stimulating an immune response. This concept is crucial in understanding the characteristics of different types of vaccines.

## Why the Correct Answer is Right
The Hepatitis A vaccine is an inactivated vaccine, made from killed virus. It does not contain live or attenuated pathogens, which distinguishes it from live vaccines like the BCG vaccine (Bacillus Calmette-Guérin), the oral poliovirus vaccine (OPV), and the MMR vaccine (measles, mumps, and rubella).

## Why Each Wrong Option is Incorrect
* **Option A:** BCG (Bacillus Calmette-Guérin) vaccine is a live attenuated vaccine used primarily against tuberculosis.
* **Option B:** Oral Poliovirus Vaccine (OPV) is a live attenuated vaccine.
* **Option D:** MMR (Measles, Mumps, and Rubella) vaccine is also a live attenuated vaccine.

## Clinical Pearl / High-Yield Fact
A key point to remember is that live vaccines are generally contraindicated in immunocompromised individuals, whereas inactivated vaccines like the Hepatitis A vaccine can often be safely administered to these patients.

## Correct Answer: C. Hepatitis A vaccine