I think this question would heavily depend on whether or not you believe that vampires and werewolves have regenerative capabilities.
Because if a vampire bites a person with an artificial heart, the virus will still be spread throughout their system/body by the artificial heart. That's what the arificial heart is for, to act like a normal heart and to pump blood through the body. And if vampires have regenerative capabilities, then the person would just eventually grow a new heart, and have to remove the artificial heart because it would be of no use anymore.
I believe it would be much the same with the werewolf. The werewolf virus (or whatever you want to consider it) would more likely than not trump that person's immune system's typical allergic response and therefore they would not have the allergy anymore.
Then again, if someone has a severe enough allergy to dogs, I believe that it could be argued that the person could die before the virus could take effect. But I haven't really heard of any cases involving a dog allery where a person dies if they get near a dog.