Vampires are a worldwide phenomenon, but the Western vampire, based out of Eastern European myth and legend and popularized by authors like Bram Stoker, is predominant, and the one people most typically think of when they hear the word. The Western vampire is also tied inextricably to religion, namely, Christianity.
All it takes is a quick listing of common vampire traits and weaknesses to see the connection: immortality through undeath, drinking blood, vulnerability to the sun, aversion to the Cross, holy water, crossing the threshold, and wooden stakes.
All of these are references to Jesus Christ in some form. Christ promised his that those that drank (symbolically) of his blood that they would gain eternal life. Vampirism is a corruption of that whereby the vampire gains an immortal existence (albeit still dead) by drinking of the blood of others. Whereas Christ was selfless in asking people to drink of his blood (giving them eternal life), vampires selfishly take blood (usually killing their victims) in order to extend themselves.
The weaknesses, too, are direct references to religion and iconography. The Cross is straightforward, as is holy water. Crossing the threshold is usually a reference to a church, and one moves onto holy or consecrated ground. In early days, extending as far back as the Jewish Passover, homes—in addition to churches and temples—were blessed and made holy in order to hold back evil. Stakes are made from local hardwoods, but the most popular woods, ash and hawthorn, are also regarded as sacred. The last, vulnerability to the sun, is quite simple as Christ is often seen as the Light of Truth, and so a simple transliteration from son to sun takes place.
Quite literally, the western vampire is a type of anti-Christ in every way, a complete corruption and perversion of the ideas set forth in Christianity.
It’s interesting, then, that so many modern vampire stories attempt to divorce themselves from the religious connection, but often the explanations fall flat. “Why do crosses not affect vampires? because it was never true.” Vampirism is relegated to a blood borne medical virus instead of something supernatural. Instead of sunlight, it’s UV. And thresholds don’t exist for many modern vampires.
What I don’t get is the why of such modern trends. But then I’m a nut for mythology, and find the religious connection of more interest. I even appreciate stories that try to extend the religious connection, like in Dracula 2000 where Dracula is Judas Iscariot, and so vulnerable to silver. Or John Carpenter’s Vampires who search for the Berziers cross that will make it possible for vampires to survive sunlight.