Well, I was contemplating horror & vampires (I mean - who doesn't at some point, right?) and wondering if I thought vampires were "sci-fi" at all - ever. Then I got to thinking about a movie I saw when I was a kid - it was called The Vampire (1957.) It's a vampire movie with a twist... a doctor accidentally takes some pills, thinking they are aspirin, but they are actually an experimental drug make from the blood of vampire bats. Of course, he turns into a bloodthirsty monster and goes on a killing spree (no sparkly, shiny, sexy bloodsuckers in this movie.) He's not your Transylvanian-type vampire either - no allergy to garlic, no aversion to crosses and no stake through the heart is needed to kill him. He ends up getting taken down by a sheriff using regular bullets. All in all - that movie scared the crap out of me!
I got to wondering why a movie like The Vampire was so much scarier to me than a movie like Dracula. (Although, honestly - I am a horror movie wimp! Can't really do them... nope... nuh, uh...) Anyway, The Vampire dealt with a man taking a pill and the pill changed him. Dracula was an undead monster who started from who-knows-where??? The Vampire has an element of Science in it... the pills were part of research that a scientist had been working on having to do with animals. So, there was a modicum of "reality" to the story.
There's less suspension of disbelief that needs to happen when there is a so-called "scientific" basis for something - like "Jurassic Park" (which, by the way, scared the bejeezus out of me!) And, even though The Vampire was a horror film - I would place it in the Science Fiction category - because of the science element. Same with Jurassic Park (book & movie) - definitely sci-fi.
So, if say - zombies - show up in a speculative fiction book, and their zombification is the result of some bio-or-chemical accident or warfare or has any kind of scientific underlying basis - is it science horror? Hmmm... I like to think so. (well, maybe "like" is the wrong word for me!)
What d'ya think?