The Vault - Fallout Wiki

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The Vault - Fallout Wiki
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For the modified FEV strain in Fallout 2, see FEV Curling-13.
Modified FEV
Modified FEV.png
Icon fev vial.png
QuestsThe American Dream
Take it Back!
Base ID0003bd33

Modified FEV is a quest item in Fallout 3.


This vial contains a modified strain of the Forced Evolutionary Virus developed by President John Henry Eden, based on the earlier FEV Curling-13 strain used by the Enclave in 2241, only now it was designed to be placed into Project Purity's water purification system.[1] According to President Eden, the virus is designed to only target super mutants, ghouls, and all other "unclean" citizens, namely anyone who had been born in the Wastelands and exposed to radiation and other mutational effects from birth. The only people who would survive the infection are dangerous radiation level free humans and humans who were born in the Vaults.

A vial of modified FEV is forcefully given to the Lone Wanderer by Eden in the hope that they will insert it into Project Purity.


In the add-on Broken Steel, if the player had chosen to contaminate the purifier with the modified FEV, what President Eden said is confirmed for as accurate and the FEV completely lethal. The medical facility of every city in the Capital Wasteland (except Tenpenny Tower and Paradise Falls) is filled with new patients dying from FEV infection. These new patients hold their stomachs and repeat dialogue along the lines of, "it burns on the inside." According to both Doctor Preston and Doctor Barrows, the FEV specifically targets the immune system of infected individuals, which in turn makes them vulnerable to other diseases. This occurs in both Humans and Ghouls, despite the latter's immunity to most diseases.[2][3] Along with affecting the immune system, the FEV severely weaken individuals both physically and mentally until it simply kills them.[4] The modified FEV is also completely undetectable by any kind of test meaning there's no possible way to screen water that has been infected as it only comes back as clean, purified water.[5]

Thankfully, the FEV is contained to only those that have ingested infected water as the transmission of FEV is impossible from physical contact or bodily fluids. However, in Rivet City, Dr. Preston comments that they are burning the corpses just to be safe.[2]


During The American Dream, John Henry Eden presents the vial to the Lone Wanderer after they are through talking in Raven Rock. They are not able to leave the room until the vial is picked up.

Related quests


  • This item uses the world model of an empty Nuka-Cola bottle, likely because, as a quest item, it can never be dropped by the player.
  • It can be given to Elder Lyons for good karma if you talk to him after you've escaped Raven Rock. With Broken Steel, the modified FEV will be removed from the player's inventory if they activated Project Purity but did not give the modified FEV virus to Elder Lyons beforehand.


  1. The 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)
  2. 2.0 2.1 The Lone Wanderer: "Doc, it's crowded in your clinic. Something going around I should worry about?"
    Doctor 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)
  3. The Lone Wanderer: "Doc, it's crowded in your clinic. Something going around I should worry about?"
    Doctor 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."
    (Barrows' dialogue in Broken Steel)
  4. If the Lone Wanderer drinks four bottles of aqua pura infected with the modified FEV, they suffer increasingly negative effects (that are temporary) such as loss of strength and intelligence until the last bottle that kills them.
  5. The 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 (Fallout 3))