The Chimeran virus is a biological weapon first engineered by the Chimera. It is responsible for mutating and transforming lifeforms ranging from humans to various animal species into Chimeran hybrid strains.
The Chimeran virus and its viral strains are strongly believed to have originated from some form of artificial meteoroid which caused the Tunguska Event in June of 1908. Though still unknown, the virus was precisely formed to attack the human genome, providing ample evidence to its true nature as an extraterrestrial bio-weapon.
The Chimeran virus has a different form for every type of Chimera except certain strains such as the Widowmaker, which do not come from the virus. The larger Chimeran strains (such as the Titan) require more than one human host.
By 1957, Military Chimera have discontinued the use of the Chimeran virus, due to them having no further need of humans to be converted. Feral Chimera can transmit the virus via their bite, most notably Leapers.
The virus was originally distributed through Crawlers into a host organism and then released into the blood stream. It causes shock in its host and forces the victim into a comatose state. The Crawlers were commonly delivered by Spire missiles onto densely populated areas. After this, Carriers were sent in to convey the comatose bodies to conversion centers, where lower caste Chimera such as Menials tended to the infected hosts, encasing them in Cocoons, which advance the hosts' physical mutations. After the Cocoons "hatch" the final product which emerges is augmented with a large cooling pack. Following the conversion, the transformed host retains no trace of their former personal identity, and are completely subservient to the higher chain of the Chimeran hierarchy.
After the events of Resistance: Fall of Man, a "second conversion process" was established and exclusively focused on infected female human victims, and the results were creatures called Boilers and Hags. One of the main characters of Resistance: Retribution, Raine Bouchard was infected and mutated into a Hag. James Grayson managed to halt the conversion process by infecting the Carriers with Dr. Claude Bouchard's serum. It's unknown if this temporary conversion process was fixed, but it was replaced by the "third conversion process": Spinners.
Between late 1951 and 1953, the Crawler strain was replaced by Spinners, which allowed for a swift infection and conversion process to be undertaken upon heavily populated areas, transforming countless humans into Grims. During the invasion of the United States, the Chimera launched Spires containing hundreds of Spinners upon American cities, turning entire areas into Gray Zones. Earlier, most of these Spire attacks were launched from Chimeran airships upon American coastlines. Many towns and cities such as Twin Falls and Chicago have become virtually empty of human or any earthly life, leaving only the cocoons that the Spinners made, in which new Chimera are slowly developed.
By the events of Resistance 3, Feral Chimera serve as vectors for the Chimeran virus, transferring the pathogen into fresh human hosts through bites that will cause victims to mutate into Chimera, with symptoms of high fever and a growing desire to consume raw meat manifesting within 72 hours.
The first instance of any major effort at researching a cure or engineering some form of immunity to the Chimeran virus was first attempted by the Russian military in 1927. Under the direction of Dr. Fyodor Malikov, Russian soldiers were chosen and subjected to a special inoculation that had been laced with Pure Chimeran DNA. They later developed similar traits to the Chimera, such as superhuman strength and regeneration. However, Malikov's vaccine was disastrously flawed as the candidates unexpectedly succumbed to madness and eventually became the Cloven.
In 1950, SRPA Tactical Ops launched Project Abraham with a similar goal to the Russians' efforts at creating super-soldiers known as the Sentinels. The Project was likewise overseen by Dr. Malikov, who learned from his previous mistakes with the Cloven and utilized his experience in perfecting Abraham's goal. Test subjects were administered with the virus and an anti-virus to see if it was possible to stop the process of transformation. However, only Nathan Hale (who was injected with a Pure Chimera form of the virus) and Joseph Capelli were considered a success.
After Hale was killed by Capelli during the events of Operation Black Eden on June 26, 1953, Dr. Malikov extracted a unique form of antigen from Hale's mutated corpse and created the Hale Vaccine which finally became the cure to the Chimeran virus. Although the Hale Vaccine ensures immunity from the Chimeran virus, the virus itself is still considered a major threat for those who have not yet received the Hale Vaccine.