Kenny Fisher is a former patient at Suffolk County Hospital, who has been living in an airtight enclosure his entire human life due to a rare defect in his immune system that made it impossible for him to resist infections and disease (Severe Combined Immunodeficiency Disorder). He is played by Connor Price.
Season 3
Aidan starts to take care of him, and on the sly takes samples blood so he can be safe and clean. Kenny, a fan of horror movies, soon begins to suspect something is off, but as Aidan does not respond to the stereotypical vampire maladies, Aidan dismisses his questions, but soon realizes he may suspect otherwise. Feeling that he may be going crazy for having suspected Aidan of being a vampire, Aidan assuages Kenny's feelings of guilt by watching TV with him. However, after waking from a nightmare where he killed Nurse Kerwin, Aidan's vampiric features are brought forward, exposing Kenny to the truth. Over the next several days, Kenny presses Aidan for the truth, and Aidan finally gives in, particularly after Kenny offers his virus-free blood. However, days later, Kenny asks for Aidan to turn him. He denies the boy's request, saying it will change him forever, but Kenny can no longer emotionally live in isolation any more, and proclaims that after he turns 18 he will leave, even if his weakened immune system kills him. To that end he allows Blake to drink from him, under the pretence that she will turn him on his 18th birthday. However, she takes too much blood and severely weakens him to the point that Aidan steps in and promises he will be the one to turn him. He turns back to Blake after Aidan reveals he does not have much time left, but after Aidan's recovery he is glad to see Aidan will turn him once more. When Kenny is up for a bone marrow transplant, he gets worried of the failure rate and decides to advance his plans with Aidan, demanding that he be turned or he leaves the hospital on his own and dies from his weakened immune system. Aidan acquiesces and takes Kenny on a last day out as a teenager, including being taken along on Josh's bachelor party. However, Kenny's behavior, including glorifying his soon-to-be vampirism, causes Aidan and Josh to worry. When Kenny watches Aidan kill a vampire stripper planning to eat Josh, Kenny realizes the immortality is not absolute, but Aidan promises him that he will use all of his experiences in his past failures to make sure that Kenny has the best life possible.
Kenny's deformed vampiric state
After turning Kenny and allowing him to sleep, Aidan discovers that he had accidentally turned another human recently, and he has been drastically deformed as either a result of the virus or the werewolf blood, and soon worries that Kenny will have the same fate.
After chaining him up so everyone will be safe following his revival, Aidan goes to help Sally, and after Josh and Nora's wedding is unaware that Kenny has also been deformed after turning.
Season 4
3 months after season 3, Kenny became the new leader of the Boston vampire clan. His former deformities seem to have faded.
A few days after we've last seen Kenny, he has two of his vampire workers to go out to get Aidan, and bring him back to Kenny. Kenny is then angered that the two vampires kidnapped Aidan instead of just ask him to come back with him. With Aidan amazed that Kenny is no longer an abomination, He explains to Aidan that after a few weeks all the defects disappeared, and he returned back to normal.
Later, Kenny brings Aidan to the new version of what used to be the 'Blood Dens' where vampires could feed on human women and men. Kenny then asks Aidan if he'll help him run Boston, but Aidan declines saying he's already run Boston, first with his maker Bishop and then with Mother, and it only leads to kill, or be killed. But Kenny pleads with him, only leading to Aidan leaving, which seems to anger Kenny a lot.
Kenny's real face. He still has one yellow eye and a part of his face is still deformed.
We then find out that Kenny is the one who sent the two vampires to kill Josh. Aidan, enraged with Kenny, takes out two stakes, and tells Kenny that if he can prove he's strong, he can kill him, but Kenny doesn't have it in him. He tries to explain to Aidan that he thought that the bond between a vampire and his maker was strong, magical even, so with Josh out of the way, Aidan would have time for him, and let him in, so that he could be a part of Aidan's life as well because he is his 'Son', and that he'll leave Josh, Nora and who ever he wants alone. But then, it seems that a few of Kenny's abnormalities have returned. Kenny tells Aidan that he can't control what he looks like, but he can compel humans, as well as vampires with much ease to see his normal face, though he'll have to drink about 4 to 5 times the blood to keep compelling them, so Kenny compels Aidan to see his normal face. He then gets a call and tells Aidan they need to leave immediately.
Aidan and Kenny rush over to the new 'Blood Den' to find all of the vampires have been staked, leaving them all dust. And Kenny, being the leader of Boston is generally angered and confused why someone would kill his people. He asks Aidan if it was the werewolves, but Aidan says they'd only attack when is was close or on the full moon. So Kenny thinks it might be a plot against himself, so they check the video camera footage shot during the killings, and it turns out the killer is Aidan's own wife, Suzanna.
A few days later, Kenny shows up in Aidan's bedroom, scared that the Vampire Hunter is going after Aidan, and that he'd never let anything happen to him, and that he also can enter the house without invitation because he was born there. After trying to plead with Aidan that he needs protection, Kenny attempts to leave through the window. But, Aidan stops him, deciding he finally needed to tell Josh and Nora that Kenny is indeed still alive, as months ago Aidan promised Josh he'd kill Kenny after he almost killed Nora. After having a heated argument on the matter, Kenny asks Josh for his forgiveness, to which Josh says he needs to take a 10 mile run.
We next see Kenny as he is following Aidan around town after his breakup with Kat. He talks with Aidan about how he knows all about break ups through the multiple tv shows he's watched about it over the course of his life trapped in his bubble in the hospital. He then gets Aidan to go back to his place at Sapp n' Sons and they dine on the bagged blood he has in his fridge. They return to the house dunk on all the blood they drank, and start a 'Werewolf Dance Party' shuffling around the house, trying to keep up conversations with some of the wolves and each other. Aidan starts to complain to Kenny that he wishes he could just be with someone without anything going wrong, and how unfair it is, to which Kenny tells him he could probably erase Kat from his mind, before leaving to go talk to the beautiful Astrid. The next morning Astrid and Kenny return to the house to give Aidan his cat statue, more formally known as Dog-Cat-Man-Dude, and tells Aidan that if he wants, he can still erase Kat from his mind if he wants, to which Aidan replies kindly no.
Trivia
As of now he is the only known living defective vampire.