I know this has been said many times, but I think the "vampire trend" goes through cycles. Anne Rice's Vampire Chronicles was a little before my time (I think?), but she made them BIG in the '90's, along with Vampire Masquerade. Then Twilight came along 10 years later; albeit with a "softer" version of the bloodsucking fiends.

In my opinion, a good story trumps everything else. I don't think an agent is going to dismiss a story because the word "vampire" appears in the manuscript; especially if you're offering something more than just a vampire story. Maybe hide the fact your story has a vampire character, so at least you'll get some nibbles, and maybe an agent won't care if Joe Vampire shows up.