Smallpox was responsible for an estimated 300–500 million deaths during the
20th century alone. In the early 1950s an estimated 50 million cases of
smallpox occurred in the world each year. As recently as 1967, the World
Health Organization estimated that 15 million people contracted the disease
and that two million died in that year. After successful vaccination
campaigns throughout the 19th and 20th centuries, the WHO certified the
eradication of smallpox in December 1979. To this day, smallpox is the only
human infectious disease to have been eradicated.