In 1979, the last cases of polio in the U.S.in four states, among Amish residents who had refused vaccination.In 1993, the virus was brought into the country by travelers with polio. Polio was once one of the most feared diseases in the U.S. In the early 1950s, before polio vaccines were available, polio outbreaks caused more than 15,000 cases of paralysis each year.