What is circulating vaccine-derived poliovirus (cVDPV)?

• A. A laboratory-derived strain used only for research.
• B. A wild poliovirus strain that has mutated in under-immunized populations.
• C. Vaccine-derived strains that acquire neurovirulence and spread in under-immunized populations, causing outbreaks.
• D. A non-polio enterovirus associated with environmental contamination.

Answer: (C)

The main idea is that circulating vaccine-derived poliovirus comes from the oral polio vaccine, which contains a live, weakened form of the poliovirus. In areas with low immunization, this weakened virus can spread from person to person. As it continues to circulate, it can accumulate mutations that restore its ability to invade the nervous system and transmit between people. When those mutated descendants spread in the population and cause outbreaks, they are called circulating vaccine-derived polioviruses. They are vaccine-derived, not wild poliovirus, and they represent a problem only in settings with insufficient immunity. This differs from a lab strain or from a non-polio enterovirus, which are unrelated to the circulating vaccine-derived strains that cause outbreaks.