One of the primary areas that WHO has worked in since its inception is disease prevention, and its most notable success has been against smallpox.
Smallpox is a highly infectious disease that causes severe scarring and blindness and, in as many as 30% of cases, death. By the 10th century, the Chinese had discovered that variolation, a process of introducing material from smallpox lesions into the body of the healthy, usually induced immunity to the disease, though it caused a scar and occasionally resulted in death. In 1798, the English country doctor Edward Jenner proved that immunity could also be caused by inoculation. He used the much less severe cowpox in his work, and hence "vaccination" (vacca is Latin for cow) was born. Though the method was very effective, the smallpox vaccine was not readily available in many parts of the world until WHO launched a multi-million-dollar global vaccination campaign in 1967.
The aggressive campaign was successful, and the last natural case of infection by smallpox occurred in 1977. WHO stipulates that after a three-year period in which no naturally occurring infections occur, an area can be declared disease-free. WHO officially announced the world smallpox-free in 1980.
In 1988, WHO launched a campaign against polio, with the goal of eradicating the disease by 2005. Poliomyelitis is highly infectious and can cause paralysis within hours; it chiefly strikes children under the age of five, and can be prevented through vaccination.
Once endemic on all continents, polio is now confined to Africa and South Asia; the Americas were declared polio-free in 1994, followed by the Western Pacific region in 2000 and Europe in 2002.