Trivalent oral polio vaccine contains* type 3 virus –
**Core Concept**
The trivalent oral polio vaccine (tOPV) is a live, attenuated vaccine designed to protect against all three serotypes of poliovirus: type 1 (PV1), type 2 (PV2), and type 3 (PV3). tOPV is a crucial tool in global efforts to eradicate polio.
**Why the Correct Answer is Right**
The trivalent oral polio vaccine contains the attenuated strains of all three poliovirus serotypes. Type 3 virus is one of the serotypes included in tOPV. The vaccine stimulates mucosal immunity in the gut, where poliovirus typically enters the body, providing effective protection against all three serotypes. The inclusion of type 3 virus in tOPV is essential for achieving herd immunity and ultimately eradicating polio.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not specify the correct type of poliovirus included in tOPV.
* **Option B:** This option is incorrect because it is not a type of poliovirus serotype.
* **Option C:** This option is incorrect because it is not the correct type of poliovirus included in tOPV.
**Clinical Pearl / High-Yield Fact**
It is essential to note that the trivalent oral polio vaccine has been replaced by the inactivated poliovirus vaccine (IPV) in many countries to prevent the risk of circulating vaccine-derived poliovirus (cVDPV).
**Correct Answer: D. Type 3 virus**