In 1796, the English doctor Edward Jenner tested an idea that would change medicine. He had that milkmaids who cowpox, a mild , seemed to be from smallpox. Jenner material from a cowpox sore scratched it into the arm of a boy. , when he exposed the boy to smallpox, the boy did ill.

Smallpox is the only human disease that has been completely eradicated. In 1967, the World Health Organization an intensified campaign it. Instead trying to everyone, teams for new cases and everyone around . The natural case in Somalia in 1977, and the world was declared of smallpox in 1980.

Smallpox was one of the deadliest diseases in human history. In the twentieth century alone, it is estimated to have killed around 300 million people. Survivors were often left with deep scars, and some were blinded.

A vaccine had existed since Jenner’s work in 1796, yet the disease continued to spread in many countries for more than 150 years. When the World Health Organization launched its intensified eradication program in 1967, smallpox was still present in more than 30 countries.

The campaign’s success depended on a change of strategy. Vaccinating entire populations was expensive and difficult in places with poor roads and few health workers. Instead, teams focused on surveillance and containment: they searched for new cases, isolated patients and vaccinated everyone who might have been exposed, creating a “ring” of immunity around each outbreak.

Several features of smallpox made this approach possible. The disease spread only between humans, so there was no animal reservoir in which it could hide. Its rash was easy to recognize, and the vaccine was stable and gave long-lasting protection. In 1980, the World Health Assembly declared smallpox eradicated.

Since smallpox, only one other disease has been eradicated: rinderpest, a disease of cattle, which was declared gone in 2011. Efforts against polio have reduced cases by more than 99 percent since 1988, but the final steps have proven extremely difficult.

One reason is that many polio infections cause no symptoms, so the virus can spread silently before any case is noticed. Unlike smallpox, polio cannot be tracked simply by looking for a visible rash. Health workers must instead test sewage and investigate cases of sudden paralysis.

Social and political factors matter too. In some regions, conflict prevents vaccination teams from reaching children, and false rumors about vaccines have led some families to refuse them.

Malaria presents different challenges. It is spread by mosquitoes, which cannot be vaccinated, and the parasite has repeatedly developed resistance to drugs. For diseases like these, scientists talk about control and elimination in particular regions, while global eradication remains a long-term goal.