On December 9, 1979, the Global Commission for the Certification of Smallpox Eradication signed their names to the statement that "smallpox has been eradicated from the world."
It was the first time that a disease had been banished from the earth by the planning and action of the world's public health professionals. And it became a model for later (ongoing) efforts to eradicate polio and several lesser known diseases.
The disease only spread from human to human, so there had been an unbroken chain of infection for more than three millennia. In the 1960s, before the eradication program, more than half a million people died every year from the disease.
But in country after country, vaccination and isolation programs lowered rates of infection until the numbers dwindled to one person who was infected, the last patient.
In Botswana in 1974, it was a little girl, Prisca Elias. In Pakistan, 1976, Kausar Parveen. Rahima Banu, Bangladesh, 1976. Amina Salat, Ethiopia, 1976.
Finally, someone had to be the last person on Earth to contract smallpox, and that person was Somalia's Ali Maow Maalin.