The Krippin virus in “I Am Legend” was intended as a cancer cure, not used as a vaccine

“Remember, in ‘I Am Legend,’ the sickness didn’t make the zombies. The vaccination did.”
Factually inaccurate: The plot of the film “I Am Legend” kickstarts with the development of a genetically modified measles virus intended to cure cancer, which later mutated into a deadly form. The virus was not used for a vaccine.
The virus that created the zombies in the film “I Am Legend” was intended as a cancer cure. Named the Krippin virus, it showed initial success at treating cancer patients. However, the virus later mutated into a deadlier form and caused a pandemic. Infected people either sickened and died, or turned into Darkseekers, creatures which display many stereotypical traits of zombies in fiction. The virus was not used for a vaccine.

FULL CLAIM: “Remember, in ‘I Am Legend,’ the sickness didn’t make the zombies. The vaccination did.”


A meme containing a screenshot from the 2007 American sci-fi/postapocalyptic film “I Am Legend” carries the caption: “Remember, in ‘I Am Legend,’ the sickness didn’t make the zombies. The vaccination did.” The meme went viral on Facebook in mid-December 2020 and received more than 10,000 interactions on the platform, according to social media analytics tool CrowdTangle.

The film stars Will Smith, who plays a U.S. Army virologist named Robert Neville. Neville finds himself seemingly the last man on earth following a viral pandemic that either killed its victims or transformed them into Darkseekers, creatures that display many stereotypical traits of fictional “zombies,” such as an aversion to sunlight and cannibalistic tendencies. During the film, Neville, who is himself immune to the virus, attempts to find a cure for the virus in the hopes of reverting Darkseekers back to their human state and obtaining a key to immunity.

The claim in the meme is false. The virus, named the Krippin virus after its creator Alice Krippin (played by Emma Thompson), is a genetically modified form of the measles virus that was used as a cancer cure, not as a vaccine. This is demonstrated early on in the film’s opening. During Krippin’s news interview:

Krippin: “Well, the premise is quite simple. Take something designed by nature and reprogram it to make it work for the body rather than against it.”

News anchor: “You’re talking about a virus?”

Krippin: “Indeed. In this case the measles virus, which has been engineered at the genetic level to be helpful, rather than harmful. I’ll find the best way to describe it…if you could imagine your body as a highway, you picture the virus as a very fast car driven by a very bad man—imagine the damage that car could cause. Then if you replace that man with a cop, the picture changes. And that’s exactly what we’ve done.”

News anchor: “Now, how many people have been tested so far?”

Krippin: “We’ve had 10,009 clinical trials in humans.”

News anchor: “And how many are cancer-free?”

Krippin: “10,009.”

News anchor: “So you have actually cured cancer?”

Krippin: “Yes. Yes we have.

The Krippin virus later mutated into a form that is likened to the rabies virus in the movie and led to a deadly pandemic and the aftermath that we see in the film.

The time of this meme’s publication and the virality of this meme are likely due to the recent developments in COVID-19 vaccines, in particular the approval given to the Pfizer/BioNTech vaccine by the U.K. Medicines and Healthcare products Regulatory Agency and the Emergency Use Authorization by the U.S. Food and Drug Administration. The meme has been interpreted by some social media users to mean that the COVID-19 vaccines could cause the same problem. However, this is unsupported by evidence from clinical trials thus far. The trials have tested tens of thousands of people and have shown the vaccine to be generally safe, although people with a history of severe allergic reactions are advised not to take the Pfizer/BioNTech vaccine at the moment. Reassuringly, there have been no reports of vaccine trial participants turning into zombies yet.

Like any medical intervention, vaccines can cause side effects. However, these are typically short-lived and mild. According to the U.S. Centers for Disease Control and Prevention, the most common side effects of the COVID-19 vaccines are fever, headache, chills, and pain at the injection site. These are also observed in vaccines that have existed for years, such as the flu vaccine. These effects don’t indicate that something is wrong. Rather, these indicate that the immune system is responding to the stimulation provided by the vaccine as expected. Indeed, the temporary discomfort posed by these side effects is similar to the muscle soreness experienced after exercise, as explained in this meme.


Several scientists, including virologist W. Ian Lipkin, were interviewed in this Popular Mechanics article regarding the scientific plausibility of various aspects of the film, including the Krippin virus.

CORRECTION (17 Dec. 2020):

Unlike several other fictional virus strains, the Krippin virus did not escape the laboratory. We have corrected the article to reflect this.

Published on: 15 Dec 2020 | Editor:

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