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—you should 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 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 variola vaccinia virus (a weakened form of smallpox), was the first in history and significantly reduced epidemics. In 1952, smallpox was declared eradicated in the United States, and by 1980, it was completely eradicated worldwide, which remains a major medical achievement.

Why is this scar so special?

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