**Core Concept**
OPV (Oral Poliovirus Vaccine) is a type of vaccine used to prevent poliomyelitis, a highly infectious disease caused by the poliovirus. It is a live, attenuated vaccine administered orally to provide immunity against poliovirus.

**Why the Correct Answer is Right**
Option A, "We get quick immune response," is incorrect because OPV provides a gradual immune response, typically taking 1-2 weeks to develop. This is because the vaccine needs to replicate in the gut to induce immunity, unlike inactivated poliovirus vaccine (IPV) which induces an immediate immune response.

**Why Each Wrong Option is Incorrect**
**Option B:** This statement is correct. OPV is indeed a live vaccine, as it contains attenuated (weakened) poliovirus strains that replicate in the gut to induce immunity.
**Option C:** This statement is correct. OPV is used in epidemic situations to rapidly immunize a large population and control the spread of poliovirus.
**Option D:** This statement is correct. Maternal antibodies can interfere with the immune response to OPV, particularly in young children, making them more susceptible to poliovirus infection.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the use of OPV has declined in countries with high polio eradication efforts, as the vaccine can lead to vaccine-associated polio (VAPP) in rare cases. IPV is now used in these countries to minimize the risk of VAPP.

**✓ Correct Answer: A. We get quick immune response**