Vaccine which must be stored in the freezer compartment of a fridge is/are -a) BCGb) OPVc) Measlesd) Smallpoxe) All of the above

**Core Concept**
The storage requirements for vaccines vary based on their composition and stability. Some vaccines are heat-sensitive and require storage at low temperatures to maintain their potency and effectiveness.

**Why the Correct Answer is Right**
The vaccines listed in the options, such as BCG, OPV, Measles, and Smallpox, contain live attenuated pathogens or are sensitive to temperature fluctuations. Therefore, they must be stored in the freezer compartment of a fridge at a temperature between -50°C to -15°C to prevent degradation and maintain their potency. This is particularly important for OPV, which is a live, attenuated vaccine that can be sensitive to temperature and humidity changes.

**Why Each Wrong Option is Incorrect**
* **Option A:** BCG vaccine can be stored in the refrigerator at a temperature of 2-8°C, but it's not typically stored in the freezer compartment.
* **Option B:** Measles vaccine is usually stored in the refrigerator at a temperature of 2-8°C, but it's not typically stored in the freezer compartment.
* **Option C:** Smallpox vaccine is usually stored in the refrigerator at a temperature of 2-8°C, but it's not typically stored in the freezer compartment.
* **Option D:** This option is incorrect because it implies that all the listed vaccines must be stored in the freezer compartment, which is not the case.

**Clinical Pearl / High-Yield Fact**
It's essential to follow the specific storage instructions for each vaccine to ensure their effectiveness and prevent any potential harm to patients. Always check the vaccine's label or consult the manufacturer's guidelines for the correct storage requirements.

**Correct Answer:** . All of the above