Very little is known about this virus. It was a Tyrant virus variant[1] created by Dr. William Birkin for the use of Captain Albert Wesker for him to fake his death in 1998. This virus increases the metabolism of its hosts, giving them incredible strength, speed and regenerative abilities. The test subject does not suffer from the rigor mortis which affects ordinary t-virus victimes, meaning Birkin found a way of perfecting the replication of cells even when the body is under extreme duress. The only known host of the virus is Wesker, so most knowledge of its effects comes from observing him.
The virus also limits itself to muscle tissue and the lower organs, leaving the brain relatively intact. This breakthrough means that the subject’s mind is retained and no ill effects take place. However, the only known test-subject (Wesker) is a known sociopath with at least six counts of 1st degree murder, multiple counts of 2nd degree murder, attempted murder, manslaughter, involuntary manslaughter, approximately 150,000 counts of corporate manslaughter, violation of international law under the Biological Weapons Prohibition Pact, conspiracy to commit genocide, bribery, blackmail and various firearms offenses. While he was clearly a naturally power-hungry, amoral individual, whether or not the virus made Wesker more prone to sociopathic behavior is ambiguous.
The virus has a unique effect on ocular tissue. The only visible effect of the virus is the way in which it affects the subject’s eyes (the pupils become slitted and cat-like, and the irises turn a brilliant yellow or red color). Wesker demonstrates the ability to move faster than the human eye can see, at least in short bursts. The only way to move accurately at such extreme speeds would be by viewing the world in hundreds of frames per second, most likely in the same range as birds. However, he is also capable of interaction with the world with the ‘normal’ speed of a human, means viewing the world in the tens of frames per second. This would indicate that the subject has voluntary control over their visual perception, or else his eyes automatically adjust to the speed at which he is moving.
It should be noted that the virus may not be a version of the T-virus at all, and may in reality be the Progenitor virus. This hypothesis is supported by Ozwell E. Spencer's claim in Resident Evil 5 that the Wesker children were to be "given birth by the Progenitor virus." Additionally it is stated in the game's archives that Wesker was administered the same virus as the other children by William Birkin, insinuating that Birkin lied to Wesker about the nature of the virus in order to carry out his orders. Finally, Ndipaya legend states that those who consume the "Stairway to the Sun," the origin of the Progenitor virus, and survive, gain amazing strength, as Wesker obviously has.
The virus is very unstable, so the host has to use a special serum to keep it under control. The serum itself must be given in very precise dosages, lest it act like more of a poison and weaken the virus user rather than strengthening their abilities while keeping the virus in check.