Smallpox, once a deadly and highly contagious virus, killed 3 in 10 infected people and left many survivors with permanent scars. Caused by the variola virus, the disease was eventually defeated through a groundbreaking vaccine made from a related virus, vaccinia.

The vaccine, which triggered a strong immune response, left a distinct scar—usually a small, round mark on the upper left arm. This resulted from a special two-pronged needle that repeatedly punctured the skin, causing a scab and, ultimately, a scar.