What distinguishes vaccine-derived polioviruses from wild poliovirus?

• A. The vaccine-derived polioviruses are the naturally occurring strains
• B. Wild poliovirus is the naturally occurring strain, while vaccine-derived polioviruses arise from mutations of the live attenuated vaccine
• C. They are the exact same virus with no genetic differences
• D. Vaccine-derived polioviruses are derived from a different virus family

Answer: (B)

The key idea is origin and genetic change. Vaccine-derived polioviruses come from the live attenuated polio vaccine strain that can replicate in the gut and spread in a population. Over time, as this vaccine virus passes through people, it can accumulate mutations and, in some settings with low immunity, regain properties similar to wild-type virus, potentially causing paralysis. Wild poliovirus, on the other hand, is the naturally circulating strain that is not derived from the vaccine. So the distinction is that vaccine-derived polioviruses arise from mutations of the live attenuated vaccine, while wild poliovirus is the naturally occurring strain. (Note: this distinction specifically involves the oral polio vaccine; the inactivated polio vaccine does not generate vaccine-derived viruses.)