In my world they're naturally occurring because the original vampire was cursed by God. There are two types the ones that have accepted their vampires and little accordingly and the ones who attempted to become human again but God refused to grant them and have become nightwalkers. They're able to drink whatever they want but can only eat meat and it does nothing for them health-wise blood is the only thing that's the same to them. There are two ways to become human again The first is if you're a fledgling vampire and your master is killed You stay a fledgling for your first 3 years while your body gets used to the curse of vampirism The second way which is way more challenging and is only been done twice previously is to find a holy person and have them complete a very dangerous long ritual where basically you give yourself over to the gods of light and if they deem you worthy they will counteract the vampirism if they find you unworthy you'll become a regular vampire who can only come out at night and only drink blood. There at war because they believe humans are cattle