- 1924-1925 smallpox outbreak and mass vaccinations in Duluth, Minneapolis, and St. Paul: http://www.mnopedia.org/event/smallpox-epidemic-1924-1925
- 1947 smallpox outbreak and mass vaccinations in New York City: http://www.virology.ws/2009/12/22/smallpox-in-new-york-city-...