The Passage by Justin Cronin. From Amazon: "You don't have to be a fan of vampire fiction to be enthralled by The Passage, Justin Cronin's blazing new novel. Cronin is a remarkable storyteller (just ask adoring fans of his award-winning Mary and O'Neil), whose gorgeous writing brings depth and vitality to this ambitious epic about a virus that nearly destroys the world, and a six-year-old girl who holds the key to bringing it back."