Before a concerted worldwide effort was undertaken to stamp it out, smallpox was the scourge of the developing world — among the most feared or any diseases, arguably, because it respected no classes or borders. Ruling classes living in relatively clean environments were liable to be struck with it as much as peasants in the countryside. In Europe the disease was more or less contained after Edward Jenner’s introduction of the vaccine; in Asia and Africa it ran rampant until the U.N. and W.H.O. took up mass vaccination programs.

On this day, October 26, 1977, smallpox was finally eradicated, with the last known occurrence taking place in a remote village in Somalia.

Vaccination programs in Africa and Asia were not universally welcomed. Some of the local administrators did not trust them or were just apathetic;  others in the civilian population were openly hostile. Fortunately the programs did not need to capture 100% of the people to be successful — a critical mass of people, around 85%, is typically enough to create “herd immunity” for the unvaccinated ones.