From winter, plague and pestilence, good Lord, deliver us.—Thomas Nashe, Autumn, 1600
SMALLPOX—AN ANCIENT enemy, seemingly vanquished in one of the great achievements of 20th-century medicine. In an unprecedented global campaign to eradicate a disease by mass immunization, led by the United States and the former Union of Soviet Socialist Republics under the auspices of the World Health Organization, a virus thought to have killed more human beings than any other infectious agent since the dawn of recorded history was wiped from the face of the earth by 1977.1 In 1980, the World Health Organization certified smallpox as eradicated, 2 and smallpox vaccination was discontinued. By international agreement, stocks of smallpox virus would be voluntarily destroyed to avert accidental release and spread.3