Hi. In the V Wars world, vampires are people with an activated predator gene. So, vampires were known long before the series events, and, based on the legends of different locations, the description of the vampires is different. At the V Wars venue, most people turned up into the bloods (as they called themselves). Bloods are bloodthirsty, savage, and mainly kill people when feeding. Mila and Danika are of Slavic origin, and they are verdulaki, vampires who inject their victims with some toxin, then feed on catatonic victims, but don't have the urge to kill them.
Verdulak or Werdulak's are vampires more in line with what Bram Stoker immortalized in his novel. They feed on blood, injecting a drug of sorts into their victims, making them more susceptible to manipulation and mental control. Instead of killing their victims, the bitten become more beholden to the verdulak for life (like a drug addict). They also can pass for human more easily, like a strigoi.
The benefit of using Jonathan Maberry's source material is that he has done extensive research on vampires and werewolf legends across the globe and can draw on that, although the verdulak seems to be a new hybrid creation for the series.
Edit: I stand corrected - Verdulak have a history at least as long as this - a movie that features a verdulak - https://www.imdb.com/title/tt0057603/reference
And it appears the reference in the film might come from an 1839 French novel by Tolstoy, "The Family of the Vourdalak's," the novel word coming from a mistranslation of the slavic term for shapeshifting vampire.
What do you think?