Will I write a Vampire story? And if I do ... then, what? Well, I would have my vampire hunters carry supplies of saline solution blessed by a priest -- for medical saline is most assuredly water, and once blessed and intravenously infused into the body it would turn the vampire hunter into an unassaible creature. 'Drink my blood and ... die!' Such men and women would wade fearlessly into vampire nests.
Or (the best writing always starts with an or) ... would they? Maybe some vampires would prefer blood whose plasma was mingled with holy water. Maybe that would be like a really really spicy curry to a human.