As a child, I once noticed a strange scar on my mother’s upper arm—a circle of small indentations around a larger mark. It caught my attention for a while, but like many childhood questions, it eventually faded from my mind.

Years later, I saw the exact same scar on an elderly woman I was helping off a train. The memory came rushing back, and I finally asked my mother about it. Her answer was unexpected: it was a mark left by the smallpox vaccine.

Smallpox was once one of the deadliest diseases in human history, caused by the variola virus. It spread rapidly and killed around 30% of those infected, often leaving survivors with permanent scars. For centuries, it caused widespread suffering across the world.

Everything changed with global vaccination efforts. The disease was officially eradicated in 1980, marking the first time humanity eliminated a major infectious disease. Routine vaccinations were eventually stopped, making the distinctive scar far less common today.

Unlike modern vaccines, the smallpox vaccine used a special two-pronged needle to puncture the skin multiple times. It introduced a live but less dangerous virus called vaccinia, causing a blister that healed into a permanent circular scar—a lasting symbol of protection and one of medicine’s greatest triumphs.