It is hard to say which has had the greater effect on the course of historic events: the actions of specific individuals, or the external forces beyond human control. “Man plans and God laughs,” goes the Yiddish proverb. This is as true for tsunamis and hurricanes as it is for deadly outbreaks of infectious disease.
In the decades since mass vaccination put an end to polio in this country in the middle of the 20th century, we have mostly been spared fast-moving, deadly epidemics. It is, however, worth remembering that we still are vulnerable, especially to viruses such as influenza for which effective treatment may not exist or be widely available.