Forced Evolutionary Virus

FEV or Forced Evolutionary Virus is a pathogen created before the Great War, used by various groups such as the Master, the Enclave, Vault-Tec, and the Institute.

West-Tek Pan-Immunity Virion
To counteract biological weapons, the United States government began the Pan-Immunity Virion Project in 2073. The project aimed to alter uninfected DNA so that it was no longer susceptible to standard viral infection.

In March 2075, the panimmunity virion was renamed FEV and Major Barnett ordered experiments focused on the quad-helix structure of the virus, which resulted in the subjects' immunity to infection and radiation exceeding expectations. Chloroplasts were not affected by the virus and Barnett canceled all future experiments concerning plant cells.

Throughout the rest of 2075 and 2076, the team experimented on flatworms, insects, mice, rabbits, raccoons, dogs, and chimpanzees. Side effects of abnormal growth rate and increased brain activity were noted in all subjects. The tests on dogs resulted in increased aggression without intelligence increase. The chimpanzee subjects were subjected to radiological and chemical agents in an attempt to create cancers, but these tests were unsuccessful.

Mariposa Military Base
In 2077, the military built a large facility in central California, the Mariposa military installation, to continue research on volunteer human subjects from the military. When the project was transferred in January 2077, the scientists who conducted the animal trials noted their disapproval regarding utilization of human subjects. Robert Spindel and Roger Maxson led the security team at the facility. FEV was not used in the government Mission Cloacina project due to sterility in the resulting creatures.

Characteristics
The virus is not airborne and only transferable via injection or direct physical contact with FEV samples. It copies DNA patterns, attempting to correct the DNA of the individual. If the individual's DNA is damaged by radiation, it will cause organ failure and death. If the subject does not have pre-existing radiation damage, the virus causes an increase in muscle and brain mass, but also causes loss of memory.

The virus causes a painful transformation, but who are infected with the virus also experience side effects such as immunity to disease and radiation. Cell death is offset by augmented growth, extending lifespans indefinitely.

The FEV cannot be removed once infection has occurred, but the Institute scientist Dr. Brian Virgil created a serum to reverse the mutation, called a retrovirus. Virgil stated that this serum would only work for one strain of FEV, and that generalizing the formula could take decades.

The Master
Richard Grey's audio diary is found in the Mariposa Military Base, which describes a first hand account of mutation after he was knocked into vats of FEV by a crane. He describes the green slime that he was immersed in and that it is the source of all the mutations his group traced to here. He wrote that at first, his skin peeled and festered, and the experience was painful. He recounted how he regained his ability walk and felt stronger, and described the experience of a tendril growing from his stomach which he used to consume other creatures.

Grey commented that he had previously thought his mind was slipping into hallucinations, but now was improving. In an attempt to see if animals would also gain awareness from the virus, Grey dipped a rat and a dog into the vats, and they became fused together. At this point, Grey stated he was "much more than a human now" and began commenting on his plans to "bring others into the glory that is the Unity."

Once Grey developed a neurolink into the military base's computer, he learned that the virus was called FEV and began to intentionally modify himself by way of injecting the virus into his body. He dipped humans that he caught into the vats, but described them as disappointments, the virus mutating them into "big and dumb mutants." When Grey caught and mutated a human that had less radiation damage, he noted that the conversion was more successful. He then sought to expand to a new "unification center" in order to continue his vision.

Grey subsequently began calling himself the Master and sought out radiation-free humans to transform into super mutants using what he referred to as FEV-2. One of the Master's direct reports, the Lieutenant, explained that the virus itself was mutated by radiation after the war, and that humans living in the wasteland that have been exposed to this mutant FEV, inoculating them from the full effects. Individuals such as those living in vaults have limited exploded to this mutated virus and are still susceptible to its effects. In addition to dipping subjects in the vats, some were experimented upon with FEV, the virus injected into various parts of the brain.

Enclave FEV Curling-13
The Enclave Chemical Corps under Charles Curling isolated the most toxic elements of the virus found at Mariposa. The scientists turned it into an even more fatal substance known as FEV Curling-13 that only impacted humans. Inhabitants of Arroyo and Vault 13 were kidnapped and subjected to tests, of which the vault-descendant subjects of the village were all killed using .0001% aerosol solution. Those from Vault 13 suffered subdural hemorrhaging and convulsions within one hour of exposure, and death within 14.5 hours.

Virus production goals were 250,000 gallons within six weeks, allowing for the murder of all non-Enclave residents in the area and around the globe, carried by the jetstream. An inoculation was developed that protected against the virus, tested on those taken from Vault 13. This immunity would be rendered to members of the Enclave staff via the air system and was also available by injection.

Enclave Modified FEV
The Enclave contingent in the Capital Wasteland utilized a modification of FEV at the behest of President John Henry Eden. This modified FEV was created in an attempt to murder individuals living in the area by contaminating the water supply using the Project Purity facility. President Eden states that the only people who would survive the infection are members of the Enclave and those who were born in the vaults. According to both Doctors Preston and Barrows, the modified FEV specifically targets the immune system of infected individuals on a cellular level. Barrows mentions that ghouls are usually immune to diseases, but are impacted alongside humans. The modified FEV is undetectable in water that has been infected.

Edgar Blackburn
In 2104, Dr. Edgar Blackburn, a former employee of West Tek, hoped to undo West Tek's creation of the super mutants and reinvent humanity using FEV, no matter the cost. His motive was to use FEV to benefit humanity to help humanity thrive in the wasteland against threats such as creatures and the radiation. Blackburn began working with Jain, Farha and Nellie Wright to see if they could improve the FEV virus as a means to help humanity thrive in the wasteland. In doing so, they conducted harsh experiments in Vault 96 on non-consenting abducted people such as Cassie Halloway. In order to acquire human test subjects, Blackburn contracted with a group of mercenaries called the Hellcat Company who did not question the ethics of his work.

The Institute
Commonwealth super mutants are the result of the Institute's research into FEV, which has continued since the early 2220s in a dedicated facility. The original goal was the creation of a successor to second generation synths by creating a new breed of super mutant that would serve the Institute as laborer and soldier. Due to a lack of success with mutants, efforts were refocused with the goal of creating third-generation synths. The organic synth project was spun off from the FEV research initiative around 2227 (the acquisition of Shaun), while the FEV research effort continued for several more decades. Both women and men were abducted from the Commonwealth and submerged in the Institute's modified FEV, their mutations carefully tracked. Successful mutations would be monitored to ensured survivability, then tagged and discarded. In layman's terms, the Institute was simply releasing super mutants into the wild, creating a scourge on the Commonwealth that lasted for years. When Brian Virgil succeeded Dr. Syverson as head of the project in April 2286, it became evident that FEV experimentation ran its course and served no useful purpose, not with the availability of third generation synths. Eventually, as Virgil's conscience took its toll, the scientist lodged a formal complaint with the Directorate. When no reaction came, Virgil rebelled and escaped the Institute after transforming himself into a super mutant, destroying as much of the project as he could.

FEV in the Capital Wasteland
Despite Vault 87 being the main research facility, Dr. Weston Lesko found another source which he used to try to de-mutate the giant ants of the Capital Wasteland. As of 2277 his efforts culminated in the creation of fire ants. Also as of 2277, the levels of the said toxin were low in the vault, so the super mutants were actively searching for it in the surrounding areas.

Behind the scenes
The Forced Evolutionary Virus is mentioned in the Fallout Bible.