Smallpox was an infectious disease caused by either of two virus variants, Variola major and Variola minor.[1] The disease is also known by the Latin names Variola or Variola vera, derived from varius ("spotted") or varus ("pimple"). The disease was originally known in English as the "pox"[2] or "red plague";[3] the term "smallpox" was first used in Britain in the 15th century to distinguish variola from the "great pox" (syphilis).[4] The last naturally occurring case of smallpox (Variola minor) was diagnosed on 26 October 1977.[5]