Smallpox, a deadly viral infection, caused severe fever and skin rashes, killing 3 in 10 infected individuals. Survivors were often left with facial scars. The disease was caused by the variola virus, but scientists developed a vaccine using the related vaccinia virus, which helped the immune system fight smallpox,

This breakthrough led to smallpox eradication by the early 1950s, ending routine vaccinations in the U.S. by 1972. The vaccine, delivered with a bifurcated needle, triggered an immune response, forming a scab that left a distinctive scar. Today, only those in high-risk labs receive the vaccine.