When I was a child, I noticed a peculiar scar on my mother’s upper arm — a ring of small indents surrounding a larger one. It fascinated me for a while, but like many childhood curiosities, I eventually forgot about it.

Years later, while helping an elderly woman off a train, I noticed the same type of scar in the same spot. My curiosity returned instantly. When I asked my mother about it, her answer surprised me: it was from the smallpox vaccine.

Smallpox was a deadly viral disease caused by the variola virus. It spread easily and killed about 30% of those infected, leaving survivors scarred for life. For centuries, it devastated populations around the world. Thanks to global vaccination campaigns, smallpox became the first disease ever eradicated. The World Health Organization (WHO) declared it eradicated in 1980, and routine vaccinations in the U.S. stopped years earlier, in 1972.

The smallpox vaccine was unlike most modern vaccines. It used a bifurcated needle, a small two-pronged instrument dipped into the vaccine solution. The skin was pricked several times quickly, introducing the vaccine into the dermis.

The vaccine contained a live virus called vaccinia, related to smallpox but far less dangerous. After vaccination, a blister formed, then scabbed and healed, leaving behind the distinctive circular scar recognized around the world.

For many, that scar became a symbol of protection—a visible reminder that they were immunized against one of history’s deadliest diseases. Today, few people under 50 have the mark, as smallpox vaccination is no longer needed.

The eradication of smallpox stands as one of humanity’s greatest medical victories. Those who still bear the smallpox scar carry a living piece of history—proof of science’s triumph over a once-unstoppable killer.