**Question:** Trivalent oral polio vaccine contains, type 3 virus -

A. Polio virus
B. Measles virus
C. Rotavirus
D. Hepatitis A virus

**Correct Answer:** A. Polio virus

**Core Concept:**
The polio vaccine is a crucial tool in the fight against poliomyelitis, a viral infection caused by the enterovirus called poliovirus. There are three types of poliovirus: Type 1, Type 2, and Type 3. Trivalent oral polio vaccine (OPV) is an inactivated form of the three types of poliovirus, which are present in the vaccine as live attenuated forms.

**Why the Correct Answer is Right:**
Trivalent oral polio vaccine contains Type 3 poliovirus as one of its components. The vaccine is made from attenuated strains of all three types of poliovirus (Type 1, Type 2, and Type 3) to provide immunity against all three types. The vaccine is orally administered, which aids in the stimulation of the immune system and promotes the development of intestinal immunity. The vaccine works by infecting the intestinal tract, allowing the body to mount a response against the virus, protecting against future polio infections.

**Why Each Wrong Option is Incorrect:**

A. Polio virus (incorrect): As explained, the correct answer is Type 3 poliovirus, not the polio virus itself.

B. Measles virus: This is unrelated to polio and is not included in the trivalent oral polio vaccine. Measles virus causes measles disease rather than polio.

C. Rotavirus: This is a separate virus causing gastroenteritis, not polio. Rotavirus vaccine is administered separately.

D. Hepatitis A virus: This is a different virus causing hepatitis, and the vaccine for hepatitis A is administered separately.

**Clinical Pearl:**

The trivalent oral polio vaccine is an effective tool in preventing polio infections. By ingesting the attenuated poliovirus strains, the immune system is activated, leading to the development of intestinal immunity and protection against polio. Understanding the correct components of the vaccine, in this case Type 3 poliovirus, is essential for correctly identifying the correct answer. When discussing the wrong options, it is crucial to differentiate between the vaccine components and viruses causing other diseases to avoid confusion.