What risks are associated with oral polio vaccine in under-immunized populations?

• A. OPV provides complete protection with no risk
• B. Vaccine-associated paralytic poliomyelitis (VAPP) and circulating vaccine-derived poliovirus (cVDPV)
• C. OPV causes disease only in non-immunized adults
• D. OPV cannot replicate in the gut

Answer: (B)

The main idea is that the oral polio vaccine uses a live, attenuated virus that replicates in the gut and is shed in stool. In populations with low immunization coverage, that shed virus can continue to circulate and accumulate mutations. Sometimes the attenuated virus reverts to a form that can cause paralytic poliomyelitis, leading to vaccine-associated paralytic poliomyelitis (VAPP) in vaccine recipients or contacts. If circulation persists in under-immunized communities, the virus can spread and become circulating vaccine-derived poliovirus (cVDPV), potentially causing outbreaks. So, the risks in under-immunized populations are VAPP and cVDPV. The other statements aren’t accurate because OPV is not risk-free, it can cause disease under certain conditions, and it does replicate in the gut as part of how it induces immunity, which is also how these risks arise.