The last case of naturally acquired poliovirus in the United States occurred in which year?

• A. 1979
• B. 1989
• C. 1969
• D. 1959

Answer: (A)

This question tests the timeline of wild poliovirus transmission in the United States. The last naturally occurring case of poliovirus infection in the U.S. happened in 1979. That year marks the point at which endemic transmission of wild-type poliovirus was interrupted domestically, thanks to widespread vaccination programs that halted person-to-person spread. Since then, polio in the U.S. has not resulted from locally acquired wild poliovirus, though rare cases can occur from imported strains or, in underimmunized communities, from vaccine-derived poliovirus. The other years don’t reflect the end of endemic wild poliovirus transmission in the United States.