Which statement best distinguishes VAPP from cVDPV?

• A. VAPP is a rare paralytic illness caused by reversion of Sabin vaccine strains to neurovirulent forms in the vaccinated person or contacts; cVDPV are vaccine-derived strains that acquire neurovirulence and spread in under-immunized populations.
• B. VAPP and cVDPV are the same phenomenon with different names.
• C. VAPP occurs only in unvaccinated individuals; cVDPV occurs in vaccinated individuals.
• D. VAPP is caused by wild poliovirus; cVDPV is caused by non-polio viruses.

Answer: (A)

The main idea here is how the polio illness is produced and how it spreads. Vaccine-associated paralytic polio (VAPP) is a rare event where the Sabin vaccine strain reverts to a neurovirulent form inside the vaccinated person or a close contact, causing paralysis in that individual. Circulating vaccine-derived poliovirus (cVDPV) is different: a vaccine-derived strain has mutations that restore neurovirulence and, crucially, it spreads in the population, leading to outbreaks in areas with insufficient immunization.

So the best statement captures both parts: VAPP is an illness caused by reversion of the vaccine strain within an individual or their contacts, while cVDPV refers to vaccine-derived strains that acquire neurovirulence and circulate in under-immunized communities. The other options either imply they’re the same thing, place VAPP only in unvaccinated people, or claim the causes are wild or non-polio viruses, which misses the distinct mechanisms and transmission patterns.