During the period of the end of magic on Earth after the destruction of the original Seed of Wonder, while the demon spirits that were responsible for reanimating and creating new vampires were still able to reanimate the bodies of those sired by vampires, they were unable to actually cross into the earthlydimension to inhabit them. As a result, all vampires sired during the period of the end of magic rose as feral, mindless creatures coined as zompires, with no trace of their human predecessors' memories and/or personalities. They were described as pack animals, preferring to fight in groups opposed to singular hunting.
Over the months following the Seed's destruction, the zompire population rose to numbers far beyond what could be maintained by the Slayer Organization or anyone else. As the zompires were too mindless to adhere to the rules that Harmony Kendall had set that had allowed vampires to be embraced by the public, the San Francisco Police Department eventually initiated an anti-zompire task force to counter them. The zompire pandemic was presumably effectively halted by the restoration of magic, when the creation of a new Seed of Wonder meant that those sired by vampires or zompires from then on instead rose as a new kind of vampire.