Vampires are undead beings who subsist by feeding on the life essence (generally in the form of blood) of living creatures.
Vampires, otherwise known as "Homonis Nocurnae" are an offshoot of humans who have branched off centuries ago after coming in contact with an unknown mutagenic virus. This exposure caused genetic changes, leading into an infinitely slower aging process, increased physical abilities, and an extremely high rate of recovery, capable of regenerating even severed limbs…but it also led to several drawbacks: vampires are deathly allergic to silver and the extract of garlic – exposure to either one sets off a rapid anaphylactic cascade, so extreme that it hyper-stimulates their cellular mitochondria, causing their cells to self-combust. They are also unable to survive any kind of UV or solar radiation; even a second's exposure causes such severe damage that it also triggers the mitochondrial cascade. Most notably, however, was the change in iron metabolism; normal humans oxidize iron at a constant rate, but vampires oxidize it even faster, causing them to constantly run out and forced to feed on human blood.
The only exception to these biological rules is Blade, who was indirectly infected with the vampire virus when his mother was bitten in the ninth month of her pregnancy; due to this indirect method of infection, Blade possesses all of the vampire's strengths and none of their weaknesses, although he must rely on a serum to resist the urge to drink blood.