You’ve probably noticed that some people have a small round scar on their upper. That is the scar from being vaccinated for small pox. This smallpox vaccine was common before 1970s. Doctors used a live Vaccinia virus so that they could trigger an immune response that would protect people against the dangerous Variola virus that caused smallpox.
Blisters form at the vaccination area after the vaccination. At first, they became crusted over, but healed in several weeks. A round scar was left in the end.
Doctors used a bifurcated needle which was dipped into the Vaccinia solution to deliver the vaccine, and the individual’s arm was poked several times. Each time the needle broke the skin, a small amount of the vaccine was deposited and blisters formed, so this probably explains why the scars are so large.