**Core Concept**
Vaccine-associated paralytic poliomyelitis (VAPP) is a rare complication of oral poliovirus vaccine (OPV) administration. It occurs due to the reversion of the vaccine virus to a neurovirulent form, causing acute flaccid paralysis (AFP) in individuals who have received the vaccine.

**Why the Correct Answer is Right**
The risk of VAPP is highest when the vaccine virus is excreted by the vaccine recipient and can be ingested by others, increasing the chance of transmission. However, the risk of VAPP occurring within the vaccine recipient themselves is also a concern. The incubation period of VAPP is typically short, with the majority of cases occurring within 1-2 weeks of OPV administration. The likelihood of VAPP decreases significantly after 28 days.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the risk of VAPP does not significantly decrease until 28 days post-vaccination.
**Option B:** This option is incorrect because the majority of VAPP cases occur within 1-2 weeks of OPV administration, making this timeframe too broad.
**Option C:** This option is incorrect because VAPP is not a common occurrence and the risk does not decrease significantly until 28 days post-vaccination.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the risk of VAPP is higher with OPV compared to inactivated poliovirus vaccine (IPV), and this risk is further increased with repeated doses of OPV. This is why many countries have switched to using IPV in their national immunization schedules.

**Correct Answer: C. 28 days**