In the mortal instruments vampirism is a result of a demon infection.
How do you become a vampire:
In the Mortal Instruments to become a vampire you first need to be killed by a vampire drinking your blood. Then within 12 hours (i think) be buried and dig your way out again. When you first emerge you will be extremely hungry.
What weakens and kills vampires:
- Vulnerable to fire
- Weakened by holy water water and other blessed objects
- Holy symbols may be anathema if the holy symbols hold weight with the specific vampire addressed. E.g. a crucifix may repel a vampire who had a christian religion before he was turned.
- Can not speak the name of God.
- Can be killed by a steak through the heart or full exposure to sunlight
A Subjugate is a human who has been fed vampire blood. A human can survive on vampire blood. Vampire blood will also greatly increase the humans lifespan but will keep them mortal. However a subjugate will be extremely obedient and loyal to his/her master (the vampire who's blood it is).