1921, America had about 200,000 cases of diphtheria; by the early 1980s, with vaccination, that had fallen to just 3. In roughly the same period, whooping cough and measles infections fell from about 1.1 million cases a year to just 1,500. Before vaccines, 20,000 Americans a year got polio. By the 1980s, that had dropped to 7 a year.