Smallpox vaccination scar on a man's arm. Smallpox is an often-fatal disease caused by the IVariola i virus. In the late 1970s a worldwide immunisation program eradicated the disease, with the last outbreak being in 1977. It was declared extinct in 1980. Prior to this it killed millions of people each year, especially in the developing world. The vaccination was pioneered by Edward Jenner in 1798. It uses the related cowpox virus IVaccinia i, from which the word "vaccinate" is derived, to prime the body's immune system against the smallpox virus. Small stores of the smallpox virus are kept in a few laboratories for scientific research.