Is DC-vampirism a viral contagion like in Marvel?
Offhand vampirism has had three origins in DC comics that I'm aware of.
1) The white wolf route, Cain the first murderer was given the mark of cain for killing Abel by God and spread vampirism.
2) Carnivore, from Supergirl, who was apparently an angel or something similar, he was a native of Heaven who left in a scheme to wrest the universe from God.
3) I believe there's a third version in which vampires were the creation of a demon, but I don't know too much about that.
Also, there's the Russian formula from I...Vampire- The Russians discovered the vector for vampirism and edited out all the weaknesses, although it's never been clear to me that just meant that they didn't need to drink blood and could go sunbathing in Hawaii or if that meant that if you tried to stake and decapitate one of these supervampires you wouldn't have a dead vampire but a lecture "What's the matter with you? Were you raised in a barn? Decapitation is just rude!"
In the comics it was presented as purely a scientific achievement, on the off chance Zoat uses it he'd probably make it alchemical in nature.
There is also Dagon of the Team Titans, a boy who was given a DNA transfusion from the corpse of Dracula, turning him into an artificial vampire.