This is a technical, medical definition of Vampires. But there were 'real' vampires throughout history, only their fetish was based on superstition and stupidity. There are many accounts of, mostly women, drinking and even bathing in the blood of young virgin girls because they though it would either keep them young or make them young. And since these people were usually the rulers of territory with villages, they had access to victims at will with no consequences.
Now, in modern times, it seems that they were not too far off from reality. I have read articles recently about the super-wealthy who are very old, getting blood transfusions using the blood of young children. Apparently, according to what I have read, it does have some salubrious effect on their metabolism.
Of course, bathing or drinking blood will have no effect (except in spreading diseases), a sterile transfusion does seem to have some benefit. So, the bloody mad-men/women of history killed innocent people for nothing, but they were not completely wrong in what they were trying to do. They sort of, had the right idea, they just didn't know how to do it right.