ya, you have to think about that as well... Maybe make different vampires with different blood capabilities, some can gain aids, but not for long do to their body and the fact that it's to cold for the virus to survive, and some have blood that has an immunity to virus' and other diseases... It's like the Vampire the Masquerade/Requiem game, they each have different characteristics about them, but are still vampires (and by characteristics, I mean have different powers and abilities, thus making them unique) which is what I think make's vampires so interesting, is because of all the different things they can do, and the fact that there's so much about them power wise that there's choices.