Why do many people have a small scar on their left arm?

If you’ve noticed a small, round scar on someone’s left arm — or if you have one yourself — know that it’s a mark left by a historic vaccine. This scar is a legacy of vaccination campaigns against smallpox, a devastating disease that has plagued humanity for centuries.
The smallpox vaccine: a turning point in medical history

Smallpox, a highly contagious and often fatal viral disease, ravaged entire populations until Edward Jenner invented the vaccine in 1796. This vaccine, developed from the smallpox vaccine virus or vaccine (an attenuated form of smallpox), was the first in history and made it possible to reduce epidemics significantly. In 1952, smallpox was declared eradicated in the United States, and in 1980, it was completely eradicated worldwide, which remains a major achievement of medicine.

Why is this scar so special?

scar

Unlike current vaccines, the smallpox vaccine was administered by a unique technique using a bifurcated needle. This needle, with two small points, pierced the skin several times to introduce a small amount of the virus into the dermis. This method created a characteristic skin reaction: a bell formed at the injection site, which eventually burst, leaving behind a scab and then a circular scar. “This scar is a testament to a time when medicine was fighting otherwise deadly diseases,” says Lydia Mammar, a medical historian.