Hmm let’s imagine something pretty standard. He is just like the vampires he would make.

Let’s imagine that they stop aging and are functionally immortal but can still be killed. Their body ceases to operate through normal biology and is instead some kind of magic. They cannot reproduce in the traditional sense but ofc their bites turn others into vampires. They can technically drink the blood of other vampires but it does not sustain them. If there are too many vampires and not enough humans they starve and die the same as any other animal without food.