The V4 Vampire Virus is a kind of computer virus created and used by Dr. Blood.
When the virus is injected into a robot's hydraulic fluid (which functions like blood), it renders the robot under the control of the evil Blood and features some vampire-like characteristics such as fanged teeth and red-orange eyes. In order to turn any infected robots back to normal, the vaccine must be injected into the first vampire that was infected by the virus. It has a side effect causing it's victims to wear shorts on their heads.
When Dr. Blood used his bot named Bat Bot to infect Saedee then later let her spread it to most of the team, Blip joins forces with a mysterious vampire-slaying bot named Hellsing V to cure his teammates. But the only way to cure the team is to stop the virus inside the first vampire who got bit by Bat Bot. In this case, it was Saedee. Blip, while vaccinated by the antivirus that Helsing created, allowed himself to get bitten and thus, cured the Thunderbolts.