Humans are vulnerable to turning by either vampires or werewolves. However, werewolves cannot turn vampires into their kind, and vice versa.

Werewolves Biting Vampires

A werewolf who bites a vampire would have no success in turning said vampire, because a vampire's regenerative qualities do not allow for virile infections. The werewolf would, however, observe an unpleasant, decayed taste to the vampire blood. There is no real harm in a werewolf tasting vampire blood, it is just highly unpleasant and if they swallow any it would likely upset their stomachs.

Because specific components of vampire blood cannot survive outside a vampire's system, ingesting vampire blood would in no way harm the werewolf carrier's virus.

Vampires Biting Werewolves

The werewolf virus cannot infect a vampire, however a vampire's system would react to the attempt at invasion by invoking its natural regenerative qualities to destroy the virus. This consumes a significant amount of energy, thus making drinking werewolf blood a losing proposition, similar to the idea of humans drinking seawater. The process of 'cleansing' the infectious blood is furthermore quite painful, causing a burning sensation in the veins.

As an aside, vampire pheromones designed to make prey more cooperative are considerably less effective on werewolves; thus a vampire may find werewolves to be a great deal of trouble to be rewarded with detrimental effects.