Why has polio returned to the United States?

Rotary has been helping to eradicate polio in the world since the 1980's. Recently, a case of vaccine derived polio was reported in Rockland County, New York, a community north of New York City. Why did this happen? What is the chance that Polio cases will be seen in our own backyard? Kris David, Rotary International End Polio Now Coordinator for parts of Canada and the East Coast of the United States, will update the club on the challenges that remain in the Global Eradication Initiative.