Vampires: Scientific Fiction or Urban Legend?

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My grandmother used to tell me stories about vampires when I was young. And it suddenly came up into my mind right now. Are vampires really true? According to my grandma, she believed that vampires were once known as warewolves. Then, these warewolves were turned into vampires when different stories from the folklore evolved. They viewed these warewolves something like a human in figure and added stories like they suck up blood of different creatures, most especially the human beings. Now, when I grew older, it came to a point that perhaps they belong to the scientific fiction. I don't really have any scientific explanations though, but do they really exist or just part of the scientific fiction?