The Last of Us Episode 9 explains Ellie’s immunity

Ellie looking at her bite wound in The Last of Us Episode 9HBO

The Last of Us Episode 9 finally explains Ellie’s immunity from Cordyceps, dealing with how she became immune in the first place and how it works – and we’re gonna break it down.

Over the course of The Last of Us Season 1, we’ve seen four different types of infected: Runners, Stalkers, Clickers, and Bloaters, with each at varying, increasingly gnarly stages of infection.

If you’re infected, you may notice symptoms such as coughing, slurred speech, muscle spasms, and mood changes. Within 5-15 minutes, it takes over your neck and head, then 2-8 hours for the torso and arms, and 12-24 hours for the legs and feet.

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Of course, Ellie is the exception to the rule: three weeks after she was bitten, all she has to show for it is a scar on her arm – so, why and how is she immune?

The Last of Us: Ellie’s immunity explained

While not explicitly confirmed, it’s implied Ellie is immune because her mother Anna was bitten while she was in labor. She cut the umbilical cord quickly after giving birth, and it’s assumed she’d already passed the antibodies to her daughter.

Ellie is bitten and scratched a few times throughout the show, but she shows no signs of infection. When Sam was bitten, she cuts her hand and massages her blood into his wound, hoping it’ll work like medicine, but it’s not that simple.

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When they get to the Fireflies hospital in Salt Lake City, Marlene tells Joel that the doctor believes the Cordyceps in Ellie has grown since birth, and it produces a “chemical messenger… it makes normal Cordyceps think that she’s Cordyceps, it’s why she’s immune.”

“He’s going to remove it from her, multiply the cells in a lab, produce those chemical messengers, and then we can give it to everyone. He thinks it could be a cure, Joel. A cure,” she explains. 

In the game, a surgeon’s recorder goes into further detail about why Ellie is the only person capable of producing a cure.

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“April 28th. Marlene was right. The girl’s infection is like nothing I’ve ever seen. The cause of her immunity is uncertain. As we’ve seen in all past cases, the antigenic titers of the patient’s Cordyceps remain high in both the serum and the cerebrospinal fluid,” the recording explains.

“Blood cultures taken from the patient rapidly grow Cordyceps in fungal-media in the lab… however white blood cell lines, including percentages and absolute-counts, are completely normal. There is no elevation of pro-inflammatory cytokines, and an MRI of the brain shows no evidence of fungal-growth in the limbic regions, which would normally accompany the prodrome of aggression in infected patients.

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“We must find a way to replicate this state under laboratory conditions. We’re about to hit a milestone in human history equal to the discovery of penicillin. After years of wandering in circles, we’re about to come home, make a difference, and bring the human race back into control of its own destiny. All of our sacrifices and the hundreds of men and women who’ve bled for this cause, or worse, will not be in vain.”

The Last of Us Season 1 is available to stream in its entirety now. You can check out the rest of our coverage here.

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