Smallpox is caused by a DNA virus of the orthopox family. It can be transmitted by aerosols, droplets, direct contact with infected skin lesions, or even contaminated clothing or linens, and spreads easily from person-to-person [62] . Humans are the only reservoir for the virus [8] . Smallpox was declared eradicated by the WHO in 1980 [62] , and routine vaccination was stopped soon afterward. The virus is officially stored at 2 laboratories of the WHO, in the U.S. and in Russia [8] , although it is possible that clandestine samples are held elsewhere. As aerosolized smallpox is extremely virulent with a low infectious dose and the easy transmission from person-to-person even in asymptomatic stages, smallpox is 1 of the most feared agents that could be used in a biological attack [62, 63] .