We are accepting new characters.  Because of how far we are into season 5, if you want a character to be very into the story, with the main characters, you would probably want to make a human or something of the sort that somehow knows about the apocalypse...or if you were going to play a vampire, you might think about playing a secondary character that is a demon or an angel.  It just makes it so that you don't get left behind in the whole apocalypse mumbo jumbo.