Magical animals? More like diseased animals.

[alethe]

Werewolves were also people with Clinical lycanthropy, a mental disorder where you think you can shapeshift into a wolf or another animal.

Vampires could also be people with the disorder Albinism, which is the lack of skin pigment. It causes pale skin, red eyes (due to lack of pigment in the eyes), and you lack the ability to produce the pigment that protects you from the sun, so you have to stay inside or wear long sleeves/pants and sunglasses. It also causes bad eyesight.

[greatdragon108]

Werewolves were also people with Clinical lycanthropy, a mental disorder where you think you can shapeshift into a wolf or another animal.

Vampires could also be people with the disorder Albinism, which is the lack of skin pigment. It causes pale skin, red eyes (due to lack of pigment in the eyes), and you lack the ability to produce the pigment that protects you from the sun, so you have to stay inside or wear long sleeves/pants and sunglasses. It also causes bad eyesight.

Albinism would be more common than Porphyria, so it was probably the start of the vampire myth. Victims of Porphyria again, are often psycho, and do lack the ability to create those pigments, which seems more like a vampire because of the psychotic behavior of the victims, but is much more rare as far as I know.
As with Clinical lycanthropy, I am wondering if this could be paired with hypertrichosis. The victim could easily be mistaken for a werewolf, especially for believers of the werewolf.
This is one of the most interesting topics I've seen yet.