What disease was the first successful vaccine developed against?

The first successful vaccine was developed against smallpox. English physician Edward Jenner introduced the vaccine in 1796 after observing that exposure to cowpox could protect people from smallpox.

Jenner’s work built on the older practice of variolation, in which material from smallpox sores was deliberately introduced to produce a milder infection. Variolation could protect against smallpox, but it sometimes caused severe disease and could spread the virus. Jenner’s cowpox-based method was much safer and became the foundation of modern vaccination.

In 1798, Jenner published his findings and helped popularize the method. The word vaccine comes from vaccinia, the Latin term associated with cowpox. Early vaccine production was not standardized, and the biological origins of some vaccine strains remained uncertain, but the approach spread rapidly through Europe and North America.

Smallpox vaccination eventually became central to a worldwide eradication campaign. The World Health Organization certified smallpox eradicated in 1980, making it the only human disease eradicated globally. Smallpox vaccination is no longer routine for the general public, although certain laboratory and military personnel may receive it.