They are the Supernatural Creature of the Late Night Expansion like the mummies of World Adventures and the Simbots of Ambitions.
I personally find them to be great additions to the game. Some people have said that Vampires are one of those features that you want to turn off but can't, as the Story Progression will automatically create Vampires in any Neighbourhood. Vampires were first introduced into the game through The Sims 3 Late Night Expansion.
The Sims 3: Vampire Vampires in the Supernatural and Late Night Expansions By Thomas Hickman (aka samoht04)
