As a child, I was fascinated by a strange scar on my mother’s upper arm—small indents surrounding a larger one. Years later, I saw the same scar on an elderly woman and finally asked my mother about it. She reminded me she’d told me before: it came from the smallpox vaccine.

Smallpox was a deadly virus that killed about 30% of those infected. Widespread vaccination led to its eradication in the U.S. by 1952, and routine vaccinations ended in 1972. The vaccine left a distinct scar because it was delivered using a two-pronged needle that punctured the skin multiple times, triggering blisters that scabbed and left permanent marks.

That scar, once common, is a lasting reminder of the disease we defeated.