In this more realistic scenario than typical fantasy, the vampire is just an ordinary human being with a certain genetic quirk that results in the following:
- A reversed circadian rhythm (active at night)
- A digestive system that accepts a more hypercarnivorous diet (in other words, meat and only meat)
- A stronger jaw with sharper teeth
Let's look up for the third point. In regards to our jaw, the width is greater than its length. For something similar, we need to look up brachycephalic breeds of dogs, narrowing the list to the Rottweiler, the breed reputed to have one of the strongest bites of any dog.
If we had a jaw more like a Rottweiler's, how strong will our bite force be? How much will the muscles in the head area change to accommodate this sort of power?