Smallpox is an acute, highly infectious, and sometimes fatal disease caused by a poxvirus and characterized by high fever and aches with subsequent widespread eruption of pimples that blister, produce pus, and form pockmarks. It is also called variola. 
Susceptibility to smallpox is based to a large degree on ethnic heritage. Europeans were plagued by it for many years and built up a resistance, whereas native American populations were decimated when European explorers reached the Americas, almost causing extinction in many areas.
Smallpox was eradicated through a mass vaccination program undertaken by the World Health Organization, and the last known case of smallpox occurred in 1977. It is tacitly acknowledged that the United States and Russia each have stores of the otherwise eradicated virus. It is not known if other rogue states, such as North Korea, may also have stores. Because of the relative danger of the vaccine, and the eradication of the illness through vaccination programs, it is not felt that vaccination should be resumed, despite the possibility of the virus's use as a bioweapon. First responders are sometimes vaccinated.