The On the Soul series was intended to be a trilogy and the third book in the series, Genesis, is in the early stage of writing. I'd taken time in between to work on another supernatural mystery series, The Friar Tobe Fairy Tale Files. There's also always the possibility of other vampire stories, related to Valery and Angelina's story, but not part of the series.
I haven't read a lot of vampire novels besides Anne Rice's Vampire Chronicles, Stephen King's Salem's Lot and, of course, Bram Stoker's Dracula and, of those others I have, most were modern vampire tales rather than historical fiction. Three vampire novels I really enjoyed are Werner Lind's Lifeblood, Ellen Maze's Rabbit and The Judging and Elizabeth Kostova's The Historian. Werner Lind's and Ellen Maze's books I appreciated especially for their spiritual aspect, but all three contain a varying degree of historical fiction, with The Historian falling the most into that category.
Thanks so much again for your questions and all the best to you.