**Core Concept**
The OPV bivalent vaccine is a type of oral poliovirus vaccine that contains two serotypes of the poliovirus to provide immunity against poliomyelitis. The vaccine is designed to protect against poliovirus types 1 and 3, which are the most common causes of polio.

**Why the Correct Answer is Right**
The OPV bivalent vaccine contains two attenuated strains of poliovirus: type 1 and type 3. These strains are designed to provide immunity against poliovirus types 1 and 3, which are responsible for the majority of polio cases worldwide. The inactivated poliovirus vaccine (IPV) and OPV bivalent vaccine are used in combination to provide broad protection against poliovirus types 1, 2, and 3.

**Why Each Wrong Option is Incorrect**
**Option B:** This option is incorrect because the OPV bivalent vaccine does not contain poliovirus type 2. Poliovirus type 2 was declared eradicated in 2015, and the vaccine is not designed to provide immunity against this serotype.
**Option C:** This option is incorrect because the OPV bivalent vaccine does not contain poliovirus type 2. Additionally, the vaccine is not designed to provide immunity against poliovirus type 2.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the OPV bivalent vaccine is used in combination with the IPV to provide broad protection against poliovirus types 1, 2, and 3. This combination vaccine is critical in areas where polio is still endemic, as it provides immunity against all three serotypes of the poliovirus.

**✓ Correct Answer: A. Polio virus 1 & 3**