**Core Concept**
Polio vaccine refers to the inactivated poliovirus vaccine (IPV) and the oral poliovirus vaccine (OPV), which are used to prevent poliomyelitis, a highly infectious disease caused by the poliovirus. The development of these vaccines marked a significant milestone in the global effort to eradicate polio.

**Why the Correct Answer is Right**
The oral poliovirus vaccine (OPV) is a live, attenuated vaccine that contains weakened forms of all three serotypes of the poliovirus (PV1, PV2, and PV3). This vaccine is administered orally, allowing the weakened virus to replicate in the gut, thereby inducing immunity against polio. In contrast, the inactivated poliovirus vaccine (IPV) is a killed-virus vaccine that contains inactivated forms of the poliovirus and is administered intramuscularly.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because OPV does contain weakened forms of all three serotypes of the poliovirus, which is true.

**Option B:** Incorrect because IPV is indeed a killed-virus vaccine.

**Option C:** Incorrect because OPV is a live, attenuated vaccine.

**Clinical Pearl / High-Yield Fact**
It is essential to note that OPV can cause vaccine-associated polio in individuals with severe immunodeficiency, such as those with HIV/AIDS or undergoing immunosuppressive therapy.

**Correct Answer:** C. OPV is a live, attenuated vaccine.