As the campaign neared its goal, Fenner and his team played an important role in verifying eradication. The last naturally occurring case of indigenous smallpox (Variola minor) was diagnosed in Ali Maow Maalin, a hospital cook in Merca, Somalia, on 26 October 1977. The last naturally occurring case of the more deadly Variola major had been detected in October 1975 in a three-year-old Bangladeshi girl, Rahima Banu.The global eradication of smallpox was certified, based on intense verification activities, by a commission of eminent scientists on 9 December 1979 and subsequently endorsed by the World Health Assembly on 8 May 1980. The first two sentences of the resolution read:

Having considered the development and results of the global program on smallpox eradication initiated by WHO in 1958 and intensified since 1967 … Declares solemnly that the world and its peoples have won freedom from smallpox, which was a most devastating disease sweeping in epidemic form through many countries since earliest time, leaving death, blindness and disfigurement in its wake and which only a decade ago was rampant in Africa, Asia and South America. Costs and benefits
The cost of the eradication effort, from 1967 to 1979, was roughly US$300 million. Roughly a third came from the developed world, which had largely eradicated smallpox decades earlier. The United States, the largest contributor to the program, has reportedly recouped that investment every 26 days since in money not spent on vaccinations and the costs of incidence.
This endemic occurrence of smallpox in Europe is of particular historical importance, as successive exploration and colonization by Europeans tended to spread the disease to other nations. By the 16th century, smallpox had become a predominant cause of morbidity and mortality throughout much of the world. There were no credible descriptions of smallpox-like disease in the Americas before the westward exploration by Europeans in the 15th century CE. Smallpox was introduced into the Caribbean island of Hispaniola in 1507, and into the mainland in 1520, when Spanish settlers from Hispaniola arrived in Mexico, inadvertently carrying smallpox with them. Because the native Amerindian population had no acquired immunity to this new disease, their peoples were decimated by epidemics. Such disruption and population losses were an important factor in the Spanish achieving conquest of the Aztecs and the Incas. Similarly, English settlement of the east coast of North America in 1633 in Plymouth, Massachusetts was accompanied by devastating outbreaks of smallpox among Native American populations, and subsequently among the native-born colonists. Case fatality rates during outbreaks in Native American populations were as high as 90%. Smallpox was introduced into Australia in 1789 and again in 1829, though colonial surgeons, who by 1829 were attempting to distinguish between smallpox and chickenpox (which could be almost equally fatal to Aborigines), were divided as to whether the 1829–1830 epidemic was chickenpox or smallpox. Although smallpox was never endemic on the continent, it has been described as the principal cause of death in Aboriginal populations between 1780 and 1870.