If you are over 45 and have a small, round, slightly indented scar on your upper arm, you have likely thought about it—perhaps a child asked about it, or you noticed it again while getting a flu shot. The short answer: it is most likely from the smallpox vaccine, and it represents a real piece of medical history. However, it does not necessarily mean what many people assume.
Large-scale studies
The scar originates from the old method of administering the smallpox vaccine: a bifurcated (two-pronged) needle was used to repeatedly
