Number of countries where smallpox was eradicated in nature 1872-1977

Edward Jenner's work on smallpox, published in 1797, was the first time that any scientific findings about vaccination were presented to the wider medical community. Within a few short years of this publication, vaccination had been practiced in most European countries, and the impact was beginning to show almost immediately; particularly in countries such as Sweden and England. As vaccination practices spread, the severity and frequency of smallpox pandemics declined, and the disease ceased to be endemic in some regions.

Iceland leads the way

Epidemics had played a significant role in Iceland's history and development throughout the pre-vaccination era. The country's geographical location meant that viruses did not spread from other countries as frequently as they did on Europe's mainland, however, this also meant that generations would reach adulthood without developing any immunity to these diseases. When these factors were coupled with Iceland's highly concentrated population, this enabled epidemics to spread rapidly throughout the population with devastating effect. The most famous of these epidemics was between 1707 and 1709, where a ship from mainland Europe brought smallpox to Iceland, and the resulting outbreak killed over one third of the entire population.
For these reasons, Iceland (although a dominion of Denmark at the time) became the first country in the world to introduce mandatory vaccination, in 1802. The Great Smallpox Pandemic of the 1870s was the last outbreak of the disease to reach pandemic level across Europe. Unbeknownst at the time, this would mark the last ever recorded case of naturally occurring smallpox in Iceland, in 1872. This made Iceland the first country in the world to eradicate the disease on a national level; the same factors that had allowed smallpox to be so devastating to Iceland's population in the past (i.e. distance from mainland Europe and a highly concentrated population) had become the reason why vaccination was so effective in the nineteenth century.

The progress of elimination

After Iceland's success, it would be another 23 years before the final smallpox cases would be recorded in any other European countries, with Sweden and Norway being the only other countries to eliminate the disease in the nineteenth century. In 1904, French Guiana was the first non-European territory to eradicate the virus, and Oceania* became the first continent to do so; with the last recorded cases in New Zealand and Australia taking place in 1914 and 1917 respectively. The United States recorded its final naturally occurring case of smallpox in 1948, and the final European case was in Portugal in 1953. Smallpox proved more difficult to eradicate in less-developed continents, due to a variety of barriers; such as dense populations and limits in infrastructure (the lack of roads made it especially difficult to combat the disease in Sub-Saharan Africa). The World Health Organization launched the Smallpox Eradication Programme in 1966, and after a number of aggressive vaccination and containment campaigns, the final case of naturally occurring smallpox was recorded in Somalia in 1977. For the next two years, scientists continued to monitor the global situation, but could find no further cases or outbreaks of the disease. On May 08. 1980, the World Health Assembly declared that smallpox had been eradicated, making it the first (and only, as of 2020) human disease to have been eradicated. This was one of the most significant and important medical developments in human history, and it has paved the way for the eradication of other communicable diseases, such as polio and measles; which are expected to be wiped out in the coming decades.