Most myths involving monsters contain truths with regard to the nature of human beings.
Werewolves for example are an attempt to explain the effect of the moon on human beings. Crime is at an all time high when the moon is full. Ancient humans didn't have X-boxes and Television so much of their time was spent paying attention to each other and the world around them. They drew logical conclusions based on what they saw and felt.
Vampires exist but not in the way they are portrayed. Vampiric people are individuals who have the power to drain you psychically. You spend time around these people and you feel mentally drained. If you are paying attention you will know who these people are. They absolutely exist and when you make the connection you'll stay away from them.
Of course the next logical question is how did these people come to be this way?...that's a whole other can of worms that might require a hub to explain.