Smallpox, or variola, was at one time one of the worst scourges ever to afflict humankind, surpassing cholera, bubonic plague, and yellow fever in time span, number of victims, and geographical coverage. The smallpox virus generally was passed from person to person in droplets discharged from the nose and mouth, and it reproduced in lymphoid tissue. It could also be transmitted by dried smallpox scabs and by articles used by a smallpox patient. After a 12-day incubation period, patients usually developed chills, high fever, nausea, aches, and a rash that filled with pus and sometimes swelled severely. Up to 40% of the patients died; in the rest, scabs eventually formed and then fell off, leaving permanent pits and scars in the skin. Some patients were left blind.
In 1796 the English surgeon Edward Jenner made a smallpox vaccine from cowpox serum, which was widely used thereafter; once smallpox was contracted, however, no specific treatment was ever developed. In 1967 the World Health Organization (WHO) began an intensive campaign to wipe out remaining occurrences of the disease, and by mid-1977 smallpox seemed to be eradicated. A few further deaths occurred in 1978 when the virus escaped from a laboratory in Birmingham, England. Worldwide efforts have since restricted the number of laboratories holding the virus for research purposes. In October 1979 the world was officially declared smallpox-free by the WHO. Scientists planned to destroy remaining smallpox strains in late 1993, but the destruction was later postponed to June 30, 1999. The vaccinia virus used to vaccinate against smallpox is now being used in the development of other vaccines.