Fenner was Director of the John Curtin School from 1967 to 1973. In 1977, he was named the chairman of the Global Commission for the Certification of Smallpox Eradication. The last known case of naturally transmitted smallpox occurred in Somalia in 1977. Professor Fenner announced the eradication of the disease to the World Health Assembly on 8 May 1980. This success story is regarded as the greatest achievement of the World Health Organization. Before its eradication, smallpox was one of the world's most virulent viruses, responsible for millions of deaths, and leaving many of the victims who survived with disfiguring scars for life.