**Core Concept**
OPV (Oral Poliovirus Vaccine) is a live, attenuated vaccine used to prevent poliomyelitis. It contains a weakened strain of the poliovirus that induces immunity without causing the full-blown disease. OPV is administered orally and provides mucosal immunity, which is crucial in preventing poliovirus transmission.

**Why the Correct Answer is Right**
OPV is effective in preventing poliomyelitis because it induces both humoral and mucosal immunity. The weakened virus replicates in the gut, stimulating the production of antibodies and immune cells that can recognize and neutralize the poliovirus. OPV also provides herd immunity, reducing the spread of the virus in the community.

**Why Each Wrong Option is Incorrect**
**Option A:** OPV does not contain a killed-virus component, making it a live vaccine. This is true and not the correct answer.
**Option B:** OPV is not administered subcutaneously; it is given orally. This is true and not the correct answer.
**Option C:** OPV can cause vaccine-associated poliomyelitis (VAPP) due to the attenuated virus reversion to virulence. This is true and the correct answer.

**Clinical Pearl / High-Yield Fact**
OPV is a critical component of polio eradication efforts due to its ability to provide mucosal immunity and reduce poliovirus transmission.

**Correct Answer: C. Vaccine-associated poliomyelitis (VAPP) is a rare but potential complication of OPV administration.**