I remember getting “ambushed” during basic training by medics with the inoculation gun. They hit us with three of them at once...two in one arm, one in the other. It hurt like hell and they don’t bother telling you what you’re getting and for what purpose.
I still have a scar on my left arm.
And I’m not getting a shot now. I don’t trust them as far as I could throw the USS Nimitz.