The conquest of smallpox.

Smallpox has been a dreaded disease for thousands of years. Recurrent epidemics traversed the known world leaving a trail of death, disfigurement, and disability unparalleled by the other great plagues. Fear of smallpox provoked the first important attempts to prevent epidemic disease by a primitive form of immunization called variolation. In 1796, Edward Jenner developed the first effective vaccine against an infectious disease by using cowpox virus to prevent subsequent infection with smallpox. The discovery of this vaccine made possible the conquest of smallpox, a task that will probably be completed this year.