There's no such thing as vampires.
That comes straight from the top. The question was decided a long time ago by the Church of Rome. Archbishop Davanzati's 1744 Dissertazione sopra I Vampiri was accepted by scholars both religious and secular, and it said Vampires were make-believe, nothing more.
The Church's problem was theological. Throughout the 18th century there had been wave after wave of vampire hysteria. Bloodsucker rumors led to mob violence, and the exhumation and mutilation of many corpses. The Archbishop of Trani, scientist and mathematician Giuseppe Davanzati, was entrusted with Rome's official investigation. He studied every vampire outbreak, becoming the leading expert on the phenomena. His Dissertazione capped a five year study and concluded that while the fantasies that inspired belief in vampires might be diabolically inspired, fantasies were all they were. Vampires were creatures born of credulity and fear. They did not exist.
Meanwhile Dom Augustin Calmet, a French Benedictine theological scholar, tackled the same question. His point of view was slightly different. Calmet was a medievalist in a scientific age. He believed that the devil could animate a corpse if it suited him, and while Dom Calmet hadn't a shred of proof, he felt there were so many reports of vampirism that there had to be something in it. He never questioned the veracity of the reports; he took them on faith. His own Dissertations was published in 1746, to scholarly condemnation.
Calmet's work was republished three times in his lifetime, and many times afterward, in several languages, including English. Davanzati's book was republished twice, both times after his death, and both times in Italian. Calmet has an extensive Wiki entry. Davanzati has none.
Davanzati made an important point: Vampires were creatures of fantasy. That, I suspect, is how they've survived, even into the modern day. People's fantasies are often more important to them than their reality.
Consider how vampires evolved. To Calmet, Davanzati, and their contemporaries, vampirism was wrapped up in religion. Calmet saw the devil at work; Davanzati saw a diabolically-inspired threat to resurrection of the flesh. If a modern horror author followed that line they'd be laughed at. This is a secular age, far more so even than the 18th century. Religion, though not dead by any means, doesn't have the hold over our imagination that it once did. To the modern era, vampirism is a virus, or a phenomenon of parapsychology. Dracula gives way to I Am Legend; both are vampire tales, but with very different premises. Even the things we think we know about vampires - stakes, garlic, sunlight - are as much creations of the film industry as folklore, and owe little or nothing to religion. Meanwhile the holy symbol, if it works at all, is symbolic not of one faith but of faith in general, on the premise that it doesn't matter what you believe so long as you believe in something.