Vampires stories tend to fall into the Urban Fantasy genre, rather than SF. And since SF tends to be about things that actually could happen, it follows that most SF magazines will not respond too well to immortal neck-biters. Better to try mags like Fantasy or Realms of Fantasy or Shimmer, who take Urban Fantasy or Science Fantasy (if you can stretch that to include vampires). Which is what he's saying, really: check out what a mag actually wants before sending it to them. Most give pretty detailed likes and dislikes. Or, if they don't (e.g. Chizine: 'Dark. Well written.'
, then you've probably got some scope. Obviously, it helps to read as many as you can before submitting. To be honest, Waxy, I'm a little surprised you sent a vampire story to Interzone: it's a pretty 'straight' SF magazine. If your story's on the horror side, I would have thought Black Static would be more appropriate.
Terry
<Added>Smiley face unintended, as always!