However, here are some fun possibilities:
* A brood of vampires
* A coven of vampires
* A nest of vampires
* A horde of vampires
* A legion of vampires
You can also be creative and invent your own:
* A shadow of vampires
* A thirst of vampires
* A night of vampires
Ultimately, the best collective noun for a group of vampires depends on the context and the specific vampires in the group.