Living persons can be contaminated by vampirism, and in rare circumstances are at risk when they die. And they cause them to die eventually. Yes I have, but only moments after exorcism has taken place. I wasn't around in the ancient world, but it is recorded by the most respected persons of the time. Tertullian speaks of the undead in the 2nd century.
Demonic interference is the reason.
No I haven't, and I wouldn't. It has been attempted, but not by me. We're familiar with just 3 dimensions and the sequence of before, now and after. The vampire is outside that, and is trapped in a twilight hell between life and death. Vampires are, it would seem, nocturnal demons.