On this date in 1954, the first mass inoculation of children against polio using the Salk vaccine began in Pittsburgh, Pennsylvania, where Dr. Jonas Salk worked. By 1979, wild-type polio was eliminated from the United States. By 1991, it could no longer be found anywhere in the Western hemisphere.
The percentage of parents refusing to vaccinate their children against disease has risen significantly in the U.S. during the last decade.