Vampires are undead immortals, originally humans that have been converted by a maker. One of their primary characteristics is the need to drink blood in order to survive.
Due to the sudden creation of synthetic blood in Japan, vampires have revealed themselves to the global population as no longer a threat to human society. Because they can drink the manufactured blood as opposed to the blood of humans, they would no longer need to prey on the human race.
Reaction to vampires varies between countries and regions. However, they are considered legal citizens within the United States, albeit with limited rights and strict rules for both races to follow under penalties like death, fang removal, imprisonment, or unwilling transformation.
Vampires are immortal and can live forever if they avoid harm, however it has been stated that 80% of vampires do not survive their first year. An example of a vampire dying young is that of Eddie Gauthier. He died because he was not taught how to glamour people. If he had been able to glamour his captors, he would have been able to escape his bonds.
The reason Bill stayed with Jessica is because new vampires do not survive well on their own as it takes time to develop and control their new vampire powers. Despite their eternal life, some vampires, as they age, begin to wish they were not vampires or try to comprehend the meaning in their life. An example is Godric, a vampire who had lived for more than 2,000 years before he decided to meet the sun.