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Forced Evolutionary Virus

Research into possible cures for the New Plague created the Forced Evolution Virus, which was further developed in an attempt to create a transmittable genetic-engineering virus -- in effect, infectious evolution.ZAX

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.


To counteract biological weapons, the United States government began the Pan-Immunity Virion Project in 2073.[1] The project aimed to alter uninfected DNA so that it was no longer susceptible to standard viral infection.[1][2]

In March 2075, the 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.[3] Chloroplasts were not affected by the virus and Barnett canceled all future experiments concerning plant cells.[3]

Throughout the rest of 2075 and 2076, the team experimented on flatworms, insects, mice, rabbits, raccoons, dogs, and chimpanzees.[4][5] Side effects of abnormal growth rate and increased brain activity were noted in all subjects.[6][7][8] The tests on dogs resulted in increased aggression without intelligence increase.[6] The chimpanzee subjects were subjected to radiological and chemical agents in an attempt to create cancers, but these tests were unsuccessful.[9][10]

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.[1] When the project was transferred in January 2077, the scientists who conducted the animal trials noted their disapproval regarding utilization of human subjects.[11] Robert Spindel and Roger Maxson led the security team at the facility, but were not aware of the nature of work conducted there.[12][13][14]

Once the inhumane nature of the research was discovered by the security team, Spindel suffered a nervous breakdown and Maxson took charge, attempting to handle the situation.[14] He ordered the scientists to be interrogated, but many conversations let to executions, and the group subsequently abandoned the base.[15][16]

West Tek research center

The virus was used in an experiment in Huntersville, resulting in the creation of mutants after the West Tek research center contaminated the local water supply with FEV in 2075.[17][18] Various strains of the virus were used in experiments on both humans and animals in the Appalachian facility.[19] Edgar Blackburn stated that observation, not a cure, was the purpose of their initiatives.[10] He was not sure what the purpose of infecting the water supply of Huntersville was, apart from this observation, as they knew the virus in its current state "produced horrors."[10][20]

Vault 87

Modified FEV was utilized as a part of the Vault 87 experiment. The scientists within the vault noted their efforts toward the Evolutionary Experimentation Program, or EEP, at the behest of Vault-Tec and the military members at Mariposa.[21] Some strains caused fatalities, and causes of death were obscured from family members.[22]


The virus is not airborne and only transferable via injection or direct physical contact with FEV samples.[23] It copies DNA patterns, attempting to correct the DNA of the individual.[24] The strain utilized in Vault 87 caused subjects of all genders to mutate into indistinguishable creatures, exhibiting identical muscle growth.[25] Brain death was a result of certain strains, where others caused skin thickening, rage, and anxiety.[26][26]

If the individual's DNA is damaged by radiation, it will cause organ failure and death.[24] 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.[24][27][28] Prolongued exposure to the virus causes individuals to develop tolerances to its effects, preventing full mutation but still resulting in side effects such as skin tone changes, as well as increased strength and stamina.[29]

The virus causes a painful transformation, but who are infected with the virus also experience side effects such as immunity to disease and radiation.[30][31][32][33] Cell death is offset by augmented growth, extending lifespans indefinitely but causing sterility.[34][35] Animals subjected to FEV grow larger in size in a short period of time.[36] 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.[37][38] Virgil stated that this serum would only work for one strain of FEV, and that generalizing the formula could take decades.[39][40]


The Unity

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.[41] 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.[42] He wrote that at first, his skin peeled and festered, and the experience was painful.[43] 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.[44]

Grey commented that he had previously thought his mind was slipping into hallucinations, but now was improving.[45] In an attempt to see if animals could also gain awareness from the virus, Grey dipped a rat and a dog into the vats, and they became fused together.[46] 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."[46][47]

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.[48] He dipped humans that he caught into the vats, but described them as disappointments, the virus mutating them into "big and dumb mutants."[49] When Grey caught and mutated a human that had less radiation damage, he noted that the conversion was more successful.[49] He then sought to expand to a new "unification center" in order to continue his vision.[50]

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.[51][52] 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 have been exposed to this mutant FEV, inoculating them from the full effects.[53] Individuals such as those living in vaults have limited exposure to this mutated virus and are still susceptible to its effects.[53] In addition to dipping subjects in the vats, some were experimented upon with FEV, the virus injected into various parts of the brain.[54]

Vault 96

Blackburn continued his work after the war in Vault 96, utilizing human subjects abducted by a group of mercenaries called the Hellcat Company in an attempt to create "perfected FEV."[55][56] Super mutants created were considered failures by Blackburn, and set free outside the vault.[57]

Enclave FEV Curling-13

The Enclave Chemical Corps under Charles Curling isolated the most toxic elements of the virus found at Mariposa.[58] An excavation team was sent to the location, shielded by protective suits, to find a supply of the virus.[29] The team collected samples of the air and soil, both of which were contaminated by the virus.[29] Local inhabitants were recruited to dig down into the facility, many of which began showing signs of FEV exposure.[29]

Once a pure sample of the virus was obtained, Enclave scientists turned it into an even more fatal substance known as FEV Curling-13 that only impacted humans.[58][59] 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.[58] Those from Vault 13 suffered subdural hemorrhaging and convulsions within one hour of exposure, and death within 14.5 hours.[58]

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.[58][60] An inoculation was developed that protected against the virus, tested on those taken from Vault 13.[61][62] This immunity would be rendered to members of the Enclave staff via the air system and was also available by injection.[63][64]

Enclave Modified FEV

The Enclave contingent in the Capital Wasteland utilized a modification of FEV at the behest of President John Henry Eden.[65] 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.[66] 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.[67][68]

According to both Doctors Preston and Barrows, the modified FEV specifically targets the immune system of infected individuals on a cellular level.[69][70] Barrows mentions that ghouls are usually immune to diseases, but are impacted alongside humans.[70] The modified FEV is undetectable in water that has been infected.[71]

The Institute

In August 2178, Dr. Frederick informed their colleague Dr. Elliott that the Directorate had pre-approved research on samples of the FEV virus which were already in their possession.[72] Scientists within the Institute engaged in FEV research were able to adapt the two most promising strains of FEV to an ideal state by 2224, releasing successful creatures back to the surface, but research subjects were exposed to radiation, causing further progress to stagnate.[72][73][74] Those working on the project such as Dr. Brian Virgil expressed their desire to close the project due to the lack of results, but were repeatedly denied.[73]

In 2287, the Institute FEV lab is identified as a potential biohazard area and has been sealed following an accident.[75] Madison Li stated that this explanation was unsatisfactory and the Director was not forthright with her concerning the situation.[76] In actuality, the experiments ended when Doctor Virgil fled into the Commonwealth.[77]


The Forced Evolutionary Virus appears in Fallout 2, Fallout 3, Fallout 4 and Fallout 76. It is also mentioned in Fallout: New Vegas.

Behind the scenes

The Forced Evolutionary Virus is mentioned in the Fallout Bible.



Fallout Cutscenes The Dipping


  1. 1.0 1.1 1.2 FEV research
  2. Return to Appalachia
  3. 3.0 3.1 FEV Experiment Disk; Log Date March 21, 2075
  4. FEV Experiment Disk; Log Date May 9, 2075
  5. FEV Experiment Disk; Log Date June 30, 2075
  6. 6.0 6.1 FEV Experiment Disk; Log Date May 13, 2076
  7. FEV Experiment Disk; Log Date January 12, 2076
  8. FEV Experiment Disk; Log Date November 9, 2075
  9. FEV Experiment Disk; Log Date October 4, 2076
  10. 10.0 10.1 10.2 Huntersville memories
  11. FEV Experiment Disk; Log Date January 7, 2077
  12. Citadel terminal entries; Maxson Family Dossiers, Roger Maxson
  13. Vault Dweller: "Base Information"
    "In light of significant advances in 2076 by the NBC on the Pan-Immunity Virion Project, the United States Defense Department, in fear of international espionage, moved a team onto the site to secure and oversee the project, now dubbed the FEV (Forced Evolutionary Virus) project."
  14. 14.0 14.1 Captain Roger Maxson's diary, October 10, 2077
  15. Captain Roger Maxson's diary, October 12, 2077: "I stopped one of the men from executing a scientist today, and demanded that we interrogate them to find out what their orders were."
  16. Captain Roger Maxson's diary, October 13, 2077: "I killed a man today. I was interrogating Chief Scientist Anderson and he was giving me the full details of their inhuman experiments. He said his orders came from the Gov't., but I didn't buy it. He started screaming about how he was following orders, how he was a military man, and I just shot him..."
  17. Fallout 76 loading screens: "The first Super Mutants in Appalachia were created right before the Great War, when West Tek poisoned the drinking water of Huntersville with the FEV Virus, in a sinister, secret experiment gone horribly wrong."
  18. Huntersville terminal entries; Gail Meyer's terminal, Personal Journal 08.20.75
  19. West Tek research center terminal entries; Advanced mutations lab terminal, Advanced Mutations Program
  20. FEV research log #5
  21. Vault 87 terminal entries, Chief physician's terminal, Entry 87-34190
  22. Vault 87 terminal entries, Engineering section, Service Issue Entry V87-007
  23. Vault Dweller: "How does the Virus work?"
    ZAX: "My research into the Forced Evolution Virus, or FEV, indicates that it is a shifting-absorptive virus. It copies DNA patterns much like RNA, storing these patterns in exons. These exons, combined with the FEV, are re-injected into the host cells in typical viral infectious fashion. This causes the host cells to 'regenerate' their DNA."
    Vault Dweller: "How do you catch FEV?"
    ZAX: "FEV is not 'caught', per se. It is not air-transmittable. Typically, infection is through injection, or direct physical contact with an FEV sample."
    (ZAX's dialogue)
  24. 24.0 24.1 24.2 Vault Dweller: "If the FEV re-infects the host with its assimilated viral patterns, how does it make a 'better specimen'?"
    ZAX: "The FEV is pre-programmed with introns of corrected DNA appropriate to the proper type of species. It therefore attempts to correct the DNA of the individual. However, as the FEV is partially reliant upon the DNA of the individual, and also includes portions of its own recursive code, the effects can be unpredictable. When inoculated into an individual with significant genetic damage, such as through radiation, it will cause the body's systems to suffer massive overhauling, leading to organ failure and death. In a genetically viable individual, it re-writes portions of DNA, causing accelerated mutation, usually leading to recursive growth due to the FEV's own patterns. This recursive growth leads to an increase in muscle and brain mass, but is often accompanied by disfigurement and damage to existing neural patterns, causing loss of memory."
    (ZAX's dialogue)
  25. Vault 87 terminal entries, Chief physician's terminal, Entry 87-34224
  26. 26.0 26.1 Vault 87 terminal entries, Chief physician's terminal, Entry 87-34233
  27. Lone Wanderer: "Do you remember who you were?"
    Fawkes: "I don't remember enough to tell you everything about my former self. My metamorphosis destroyed a good deal of my long term memory. However, I can recall being in this place when it wasn't the macabre laboratory that it's become. I remember walking around this place and seeing other humans in white lab coats and blue jumpsuits. I wish I could find out more, but the personnel information for the Vault wasn't in the mainframe for some reason. I feel like my identity is so close to me... I can almost see myself as a human but can't recollect the details. It's maddening."
    (Fawkes' dialogue)
  28. Elijah: "Dog? Hnh. Appropriate. It's what I called him. You've met him. You know why he forgot - his brain was ruined by FEV, his memory, wreckage."
    (Father Elijah/Dialogue)
  29. 29.0 29.1 29.2 29.3 Military base level 4
  30. Vault Dweller: "Why isn't FEV affected by radiation?"
    ZAX: "The FEV is a megavirus, with a protein sheath reinforced by ionized hydrogen. It is therefore capable of absorbing neutrons without becoming radioactive."
    (ZAX's dialogue)
  31. Vault Dweller: "How are you more advanced?"
    Lieutenant: "Intuitively obvious to the most casual observer. We are highly intelligent and immune to disease. The strong survive! It is our goal to improve the human race."
    (Lieutenant's dialogue)
  32. Master: "Radiation has no effect on us. The FEV virus makes us immune. Your argument is weak, and so are you."
    (Master's dialogue)
  33. Lone Wanderer: "So, tell me more about yourself."
    Fawkes: "I was born here, in this place. I don't mean that in the literal sense of course. All I can remember is the excruciating pain that tore through me as my body underwent the rapid physical changes. For most, this moment is what severs the grip on their minds. They become barely a shell of their former selves. I was different. When I spoke to them, they immediately branded me "another failure" and had me placed here as a curiosity."
    (Fawkes' dialogue)
  34. Vault Dweller: "What potential long-term side effects exist?"
    ZAX: "As the FEV causes constant regenerative update to DNA, it would effectively render the subject largely immortal, as cell death would be offset by augmented growth. Additionally, as the gametes of the reproductive system consist of 'half-cells' using split DNA, they could be perceived as 'damage' by FEV, which would 'repair' them, rendering the subject sterile. However, as my laboratory facilities are damaged beyond repair, this is conjectural. I cannot offer physical proof. You will have to, in human terms, 'take my word for it."
    (ZAX's dialogue)
  35. Citadel terminal entries; Pentagon Library terminal, Mission Cloacina Report
  36. Lone Wanderer: "Something isn't right. You shouldn't have gotten results like these so quickly."
    Weston Lesko: "Well... ummm, I may have used a few... ahem, shortcuts. Yes. I was told that the FEV works wonders when used under controlled circumstances! Apparently I was wrong, but I know my mistake. I'm certain I can get it to work!"
    (Weston Lesko's dialogue)
  37. Sole Survivor: "It'll work. Don't worry."
    Brian Virgil: "I hope so. We just have to let the retrovirus run its course. I'm going to rest for a while. Come back in a few days, maybe a week, and... well, I guess we'll see."
    (Brian Virgil's dialogue)
  38. Brian Virgil: "Retrovirus has matured nicely. Density gradient is high... Recombinant counter-intron sequences look stable... Transcriptive exon strands have formed..."
    (Brian Virgil's dialogue)
  39. Brian Virgil: "Welcome back. It needs some refinement, but I think we can consider my serum a qualified success."
    Sole Survivor: "This is a "qualified success"?"
    Brian Virgil: "There were some side effects to the process. I seem to have hair again. And I've retained some muscle mass. The genetic resequencer needs more work. Still, I take your point. This is a significant advance. But only for one strain of FEV. It will take years, perhaps decades, to generalize my formula."
    (Brian Virgil's dialogue)
  40. Vault Dweller: "Could FEV mutation be corrected with a counter-virus?"
    ZAX: "No. FEV does not retain unaltered original copies of the subject's DNA. Only a virus which re-infected the subject with original DNA could reverse the effects. Additionally, there is no known way to remove the FEV itself."
    (ZAX's dialogue)
  41. Richard Grey's audio diary; 0005 - 0020
  42. Richard Grey's audio diary; 0028 - 0043
  43. Richard Grey's audio diary; 0000 - 0004
  44. Richard Grey's audio diary; 0058 - 0096
  45. Richard Grey's audio diary; 0097 - 0111
  46. 46.0 46.1 Richard Grey's audio diary; 0112 - 0134
  47. Richard Grey's audio diary; 0135 - 0139
  48. Richard Grey's audio diary; 0154 - 0172
  49. 49.0 49.1 Richard Grey's audio diary; 0199 - 0236
  50. Richard Grey's audio diary; 0237 - 0281
  51. Vault Dweller: "FEV"
    Lieutenant: "The Vats are where the FEV is stored, and where you normals become one of us. Of course, some die horrible, excruciatingly painful deaths, but well, those are the breaks."
    (Lieutenant's dialogue)
  52. Vault Dweller: "I happen to know that your mutants are sterile."
    Master: "Preposterous! The FEV-2 virus doesn't destroy the reproductive organs of those it mutates."
    (Master's dialogue)
  53. 53.0 53.1 Vault Dweller:"Why am I a prime human?"
    Lieutenant: "The FEV was mutated by the war radiation. Those living in this desolate wasteland have been exposed to this mutant FEV, essentially inoculating them from the full effects."
    Vault Dweller: "So?"
    Lieutenant: "So, you're from a Vault and have limited exposure to this mutated virus. The original FEV in the Vats should work quite well on you."
    (Lieutenant's dialogue)
  54. Mad scientist: "It's not going well. I've been injecting the FEV directly into the pineal gland, but I'm not getting the results I'd hoped for."
    Vault Dweller: "Why don't you try injecting it directly into the Amygdala?"
    Vault Dweller: "Why don't you try injecting it into the Medula?"
    (Mad scientist's dialogue)
  55. FEV research logs; FEV research log #112
  56. FEV research logs; FEV research log #148
  57. FEV research logs; FEV research log #57
  58. 58.0 58.1 58.2 58.3 58.4 The Project
  59. Chosen One: "Great for you, but how does that have anything to do with eradicating everyone?"
    Charles Curling: "Oh, yes, well, I was getting to that. The F.E.V. virus bond is species specific, it will only bond with human glyco-proteins. It only took a few years to tweak the F.E.V. virus to make it more lethal than it all ready was. The result was just what the doctor ordered, perfect in every way."
  60. Chosen One: "Great, so you have all this poison and no way to spread it around."
    Dick Richardson: "Oh, but that's one of the advantages of the F.E.V. virus. We can release it right here and the jetstream will carry it worldwide. It'll have plenty of time to cleanse every nook and cranny of the globe."
  61. Chosen One: "A virus?"
    Dick Richardson: "Yes, the F.E.V. virus. It was originally developed to turn soldiers into super-warriors but it failed. The warriors were tough and strong, but far too stupid. However, our brilliant Chemical Corps altered it."
    Chosen One: Altered the virus? Why?"
    Dick Richardson: "To turn it into a staggeringly effective killer. Any humanoid that isn't inoculated against its effects before its release, will die. That is the Project."
  62. Chosen One: "OK. Then why did you have to kidnap my villagers and the people from Vault 13?"
    Dick Richardson: "Test subjects. Your villagers are all descended from vault stock and we had to make sure that the F.E.V. toxin was still effective. The subjects from Vault 13 test that and an inoculation against the FEV."
  63. Chosen One: "What about my people? Or me? Or you, for that matter?"
    Charles Curling: "I can release the antidote into the air-system for all the cells. The detention level is served by a separate air system from the rest of the Enclave. Everyone will think that I'm just running another test. You, I can inoculate directly, here and now. (he reaches for you with a syringe)"
  64. Dick Richardson: "You could try, I suppose, but soon the staff of the Enclave and Navarro will be inoculated."
    Chosen One: "They aren't already?"
    Dick Richardson: "We just have to distribute the supplies. A matter of hours. Besides, the Enclave is a sealed unit. No air or contaminants get in or get out."
  65. Lone Wanderer: "Where did this plan of yours come from?"
    John Henry Eden: "A great many years ago, the remnants of the government had a similar idea. I can only assume the plan failed, as I never heard word of its success. But the plan itself was sound. I've made a few modifications, and with your help, I do believe it can work. There's a bright future ahead of us, my young friend."
    (John Henry Eden's dialogue)
  66. Lone Wanderer: "My father's work? How is that relevant?"
    John Henry Eden: "The purifier your father helped create has the ability to provide clean water to the whole of this "Capital Wasteland". With a simple modification, it can be used to distribute agents that destroy mutated creatures upon ingestion. In time, we could eliminate all mutations in the Wasteland at the same time the good people of the world regain their health. I need you to make the modification necessary for this to succeed."
    (John Henry Eden's dialogue)
  67. Lone Wanderer: "Won't this kill pretty much everyone in the Wasteland?"
    John Henry Eden: "Anyone or anything that has been affected by mutation will be eliminated. You will likely be immune, thanks to your upbringing in the vault. Likewise, the good people of the Enclave will be unaffected as well. I understand that you may have become sympathetic to certain individuals in your travels. Individuals this will eliminate. Please recognize that the fate of our entire country rests on this plan. Sacrifices must be made for the greater good."
    (John Henry Eden's dialogue)
  68. Lone Wanderer: "I'll do whatever I have to if it means getting rid of mutants."
    John Henry Eden: "I was hoping you would see it my way. If the water purifier can be activated, it can be used to distribute toxins that will eliminate any mutated creatures upon ingestion. The longer it runs, the cleaner the world becomes. I need you to see that it starts running, and that the necessary modification is made."
    (John Henry Eden's dialogue)
  69. Lone Wanderer: "Doc, it's crowded in your clinic. Something going around I should worry about?"
    Dr. Preston: "Oh no... I'm fairly certain it's not contagious. Though, we are burning the bodies of the deceased, just in case... I just wish I knew how to treat these people. It's like their immune system is killing them. I don't know what to do about it!"
    (Preston's dialogue)
  70. 70.0 70.1 Lone Wanderer: "Doc, it's crowded in your clinic. Something going around I should worry about?"
    Dr. Barrows "I don't know yet. Some kind of virus that attacks the body on a cellular level. I've never seen anything like it. It's strange because ghouls are immune to almost any known disease."
    (Doctor Barrows' dialogue)
  71. Lone Wanderer: "Doc, it's crowded in your clinic. Something going around I should worry about?"
    Doctor Church: "There's something going around, all right, but it isn't anything I've ever seen before. Definitely not contagious. Maybe something in the water, but that seems unlikely since I've tested it and this is the cleanest water we've ever had. I have no idea how to help these people and it's really taken the shine off my normally sunny disposition."
    (Church's dialogue)
  72. 72.0 72.1 FEV research notes
  73. 73.0 73.1 Brian Virgil personal log 0176
  74. The Institute terminal entries; FEV Lab Entry Terminal, Subject CM-153
  75. The Institute terminal entries; FEV Lab Entry Terminal, Project Synthesis
  76. The Institute terminal entries; Institute Advanced Systems, Personal Notes
  77. Fallout 4 loading screens: "The Institute's experiments with the Forced Evolutionary Virus, or FEV, ended when Doctor Virgil went rogue and fled into the Commonwealth."