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The diagram is a graph showing measles incidence in the United States from 1961 to 1996.
There were almost 500,000 cases around 1962, the vaccine was licensed around 1966, and the cases dropped dramatically from between 1966 and 1971. After 1971, the number of cases remained under 50,000 through 1991. From approximately 1992 to 1996, the number of cases is not significant enough to appear on the graph.
Source: U.S. Department of Health and Human Services. October 31, 1997. Summary of National Diseases, United States 1996. Morbidity and Mortality Weekly Report, 45(53): 43.