Some of them are sensitive to it, but it doesn't kill them. Certainly the majority of them I know have been born mortal, and Awakened a vampire. Vampires feed on something they call pranic energy, which is a form of magickal energy, and can be found in blood, crystals, and various other sources. Some also will take energy directly from a human source, tapping into their psychic lifeforce, or psi-feeding. These vampires are known as psychic vampires.
Vampires come from all countries and races.
Such children who are born with the Warrior's Heart are often very athletic, and excel at sports. After Awakening, the call of the road often pulls them, and the new Warrior often travels extently, finding new ways of honing their combat skills. They will then defend those people for the rest of their term, for reasons known only to them. I have only known them to abort their duties when their code of ethics have been violated.