Before the eighteenth century, smallpox was a serious cause of infectious disease epidemic outbreaks. A potentially fatal illness transmitted by respiratory means, smallpox killed up to 30 percent of those infected by it. In 1796, an English physician named Edward Jenner discovered the vaccine for smallpox and, in fact, coined the term vaccine. Through vaccination, the disease was largely eradicated in the developed world by the middle of the twentieth century. Aggressive vaccination programs were subsequently undertaken in the Third World. The last naturally occurring case of smallpox was diagnosed in Somalia in 1977. Since smallpox has been eradicated as a clinical disease, it no longer causes epidemic outbreaks.