© WHO/J.F. Wickett Ali Maow Maalin, from Merca, Somalia, contracted smallpox in October 1977, the last known case of naturally occurring smallpox infection in the world. In 1980, 21 years after the global eradication campaign began, the World Health Assembly officially certifies the world free of smallpox - the first disease ever eradicated. An estimated 500,000 children are disabled by polio every year.