Vampire induced change?

Okay, I had an idea for a story, but it sounds too familiar, like I've read it somewhere before. If I have then obviously I don't want to go stealing another writer's idea. So here's the premise:

Vampires aren't created like the old stories. When there is a blood exchange the vampire's 'infected' blood actually produces a change in sex as well as all the extras that come with the legends. Call it a innate, natural, or DNA encoded defense mechanism, whatever. I haven't exactly worked that out yet.

Anyway, has a Vampire induced change been used before? I've already got a decent plot in my head, but it's just sounding too familiar. Any ideas?

Lili