Vampires are victims of the Vampirism disease, created by the Black Dragon King of Disease, Nalrut.
It's a dangerous disease, in that they'll harm the others around them, and being a Vampire can significantly shorten one's lifespan. Vampires rarely live more than 30 years, this is without drinking blood. As a Vampire, your blood would dry up extremely fast. This is why the Vampires on Zeterra must drink blood; to replenish theirs.
Being a Vampire does have it's upside, though. Vampires can grow Demonic wings, they do not need to eat or drink like a regular person, and they have slightly heightened reflexes and stamina, granting a +4 to a character's DEX, and a +1 to STR gain rolls.
But, with such abilities, there are downfalls. They do not burn in sunlight, but they grow extremely weak and tired when exposed directly to it. Any consumption of water that isn't diluted to a great extent will temporarily poison a Vampire, and they are exceptionally weak to a Werewolf's claws and teeth.
By drinking blood daily, a Vampire can extend their lifespan up to 500 years longer than they would have lived as a regular being.
Vampirism can be cured with a mixture of Dragon Blood, water, and Wyvern Venom. It can also be cured by trading with Nalrut. He is likely to ask for you to be under his service for a time, or sacrifice a Werewolf.