Vampire's don't specifically need human blood. The idea is that the virus affects the hemoglobin in their blood, creating a deficiency. They make up for this deficiency by draining the blood and therefore hemoglobin to sustain that which they don't have and need to survive. Now if someone has a cardiovascular system they will have blood and for that blood they will have hemoglobin. Assuming elves have blood they would do fine to sustain it. Vampire nerd (in yo' face)