@deany17 - I'm not a vegan myself, but I've discussed this with a friend of mine who is. (Many vegetarians eat eggs and/or dairy, and so could get B12 from that, whereas vegans don't consume any animal products.)
To be honest, I don't know how B12 reaches the parts of the body it needs from an injection. What I do know is that most vegans have no need of B12 injections. They get their B12 from nutritional yeast (yum), fortified breakfast cereals, fortified milk alternatives like soy milk, and vitamin tablets. There are plenty of ways to get B12 without eating animal products and without having shots.