In Every fictional universe vampires are different.
In Harry Potter we know little about them except that they feed of human blood, are part of the living dead Category, have long lifespans and aren't much of a problem. So what are they. Are they a normal generic subspecies of Humans or do you have to be bitten to be transformed.
Let me just say, I don't think getting transformed like werewolves is the answer. I think that if everyone transformed became a Vampire and have A longer but lower quality life, it would be to good to be true. I think dark wizards would use it to extend their lifespans all the time.
And why are they considered "Living Dead", we know resurrecting the dead is impossible. But reanimating corpses with Dark Magic is possible but the real person dies. Either it's a misconception because their heart don't beat or they are corpses reanimated with Dark Magic.
I think that in Harry Potter Vampires are a Sentient Parasite that grows inside Dead Bodies. I think that when someone is bitten the real person dies or the parasite in their body waiting for them to die from natural causes. My guess is that Vampires are along these lines.
What do you think they are?