I was meditating earlier while taking a shower,
and realized a correction could be made here.
Perhaps "half vampires" would be half awakened vampires.
They're still human,
they are still vampire,
but they would only be half way through the awakening
which is when they become aware of what they are
and the traits of vampirism begin to show.
I kind of doubt that is what was referred to,
but it's a possibility that popped into my mind
so I thought I'd share it anyways. :)