During the mid-twentieth century, the polio epidemic was so severe in the United States that tens of thousands of people were crippled by it every year. Once virologist Dr. Jonas Salk created a successful vaccine in 1955, however, those numbers began to plummet. Since 1979, there has not been a single case of wild poliovirus that has originated in the United States. (Some wild poliovirus cases have been brought to the United States from other countries.) Even today, polio cases of any kind in this country are strikingly rare.
Yet a new crop of polio cases in New York state suggests that polio outbreaks are no longer as rare as they once were in the United States.
