It had long been well known among farmers that people who worked with cows rarely caught smallpox; instead, they often caught a similar but much milder disease called cowpox. A British doctor called Edward Jenner was fascinated by this, and so he studied cowpox. He became convinced that, by vaccinating people with the disease, he could protect them against the much worse disease smallpox.

In 1796, he vaccinated a boy with cowpox and, two months later, with smallpox. The boy did not get smallpox. In the next two years, Jenner vaccinated several children in the same way, and none of them got the disease.

News of the success of Jenner's work soon spread. In 1800, the Royal Vaccine Institution was founded in Berlin, Germany. In the following year, Napoleon opened a similar institute in Paris, France. Vaccination soon became a common method to protect people against other viral diseases, such as rabies, and vaccines were sent across the world to the United States and India.

It took nearly two centuries to achieve Jenner's dream of getting rid of smallpox from the whole world. In 1967, the World Health Organization (WHO) started an ambitious vaccination program, and the last case of smallpox was recorded in Somalia in 1977.