I just spent several hours doing a large amount of research on the brain, which was leading me to formulate a possible explanation for my zombie/vampire creatures (in the forthcoming, as-of-yet-named web serial I'm working on). I was going to create some kind of virus that damaged and/or mutated certain aspects of the frontal lobes (which conveniently are still growing and changing during adolescence, providing a perfect explanation for a different effect of the virus on teenagers, should I choose to go that route), causing aggressive behavior, a loss of personality traits including speech and various other symptoms.
It was PERFECT!!!!!!!!!!
And, of course, I just discovered that Resident Evil already did it. Furthermore, they had it disseminated in exactly the way I would have--as an accidental leak for a biological weapon or research in the creation of a super soldier.
I didn't think my idea was original exactly. I knew it had elements in common with other zombie/vampire explanations. But I really thought the frontal lobe stuff was a fairly original twist. Nope.
Scott Westerfeld's already taken the parasite angle.
I'm really tempted to throw up my hands and do the whole, "No one knows why this happened!" thing, since most of my characters probably wouldn't. Or maybe I just do the frontal lobe thing anyway. But if I do, I don't think I can use a virus, and I don't think it's going to come from the army.