Scott Westerfeld said this quote

“ Sure, zombies can “be a metaphor.” They can represent the oppressed, as in Land of the Dead, or humanity’s feral nature, as in 28 Days. Or racial politics or fear of contagion or even the consumer unconscious (Night of the Living Dead, Resident Evil, Dawn of the Dead). We could play this game all night.But really, zombies are not “supposed to be metaphors.” They’re supposed to be friggin’ zombies. They follow the Zombie Rules: they rise from death to eat the flesh of the living, they shuffle in slow pursuit (or should, anyway), and most important, they multiply exponentially. They bring civilization down, taking all but the most resourceful, lucky and well-armed among us, whom they save for last. They make us the hunted; all of us.That’s the stuff zombies are supposed to do. Yes, they make excellent symbols, and metaphors, and have kick-ass mythopoeic resonance to boot. But their main job is to follow genre conventions, to play with and expand the Zombie Rules, to make us begin to see the world as a place colored by our own zombie contingency plans. ”