smallpox, also called variola major, acute infectious disease that begins with a high fever, headache, and back pain and then proceeds to an eruption on the skin that leaves the face and limbs covered with cratered pockmarks, or pox. For centuries smallpox was one of the world’s most-dreaded plagues, killing as many as 30 percent of its victims, most of them children. Those who survived were permanently immune to a second infection, but they faced a lifetime of disfigurement and in some cases blindness. But smallpox was also one of the first diseases to be controlled by a vaccine, particularly