I've got a thery. call me crazy, or stupid if you wish, but this is mearly my pondering, what if.......
I read a section in gothic grimore about demons. in this pasage it says that in the days of old, negitive energy was often formed into actual demons by the minds and belifes of the people. if they actully belived, and gave the energy a face and a name, it sometimes made an appearnce to them. prehaps this was just their imaginations, but lets just say this being had manifested. If strong belives in demons could lead to their manefetation, its possable Vampires could manifest in this way. acording to what i've come up with, the idea of vampires(even if known by another name) have been around since before civilization. if the people of long ago belived stongly enough in these vampires, a creature as such could manifest. if the manifetation was strong enough, it could make an actual phyical appearnce.
but today, with so few actully haveing full faith in the existance of these creatures, the ones made long ago would disappear.
this is reaching out pretty far, but the power of human will, and belife is very strong.
it was just an idea.