From what I understand, its that age old battle of humans against mortality and aging. It's a common theme in a lot of vampire novels, the weakness of humans, and yet their strength. We get old and frail, but we value life because its finite. Vampirism can be a symbol of human desire to be young and agile forever, hence why its portrayed as sexy and alluring, its desirable selfishness. And 吸血鬼 must drink blood to sustain it, 或者 they will too age and become frail, and thus represents our addiction to youth. It's a flaw in our human nature to seek perfection in our looks wbs to hold onto it as long as possible. Vanity = vampires.