Endosymbiont by Elizabeth Noble

A werewolf and seven vampires are all that stand between the world and complete annihilation.

When Kai Richter and Ori Bier met, sparks flew.
Then a train blew up.
Tracking an organism deadly to not only humans, but vampires and werewolves alike, brings Kai and Ori into The Vampire Guard. Decades later, they, along with Operative Team Jack Rabbit, come face to face with the horrors that same virus produces. Dead bodies are coming back to life, and rational people are becoming violent and brutal killers.
A massacre is taking place nearly a mile under the Atlantic Ocean. Two teams of The Vampire Guard are in the thick of it, fighting to survive.