Well it's said to be the smallpox vaccine
Often confused with the tuberculosis One
Some Anon said once It was a way to collect everyone's DNA...

Doesnt seem too far fetched...

Sometime in the 60's, those shots were given out at the public library. I remember standing in a line with other mothers and children to get one, I went first and my brothers were screaming they didn't want it. As it turned out right after I got mine they ran out of that batch and had to refill it... made brothers scream more.

It wasn't a syringe they used more like a gun type thing and it made a noise when you were injected.... makes you wonder if it was an injection or a skin grab.