Season One of The Last of Us on HBO has come to a close, but that doesn’t mean that there isn’t some major discussion to be had. The show dives deep into the backstory of Ellie’s birth to shed light on what events could have led to her immunity, and the question is finally directly answered via Marlene’s conversation with Joel in the Firefly hospital. Let’s take a look at the reason why Ellie is immune in The Last of Us.
Did The Last of Us explain why Ellie is immune?
The player is never presented with a definitive answer as to why Ellie is immune in The Last of Us video game. The show, on the other hand, gives the audience the necessary backstory and information needed to solve the riddle. Ellie is immune to cordyceps because it has grown inside of her since birth, and signals to actual cordyceps that she is already infected.
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Marlene explains this to Joel when he wakes up in the hospital after the Fireflies knock him and Ellie out. Ellie is being prepped for surgery, as is the case in the game. When Joel asks to see her, Marlene explains that the cordyceps inside of Ellie since birth acts as a sort of chemical messenger to the real cordyceps, relaying that she is also a part of the infected, which triggers no reaction from the fungus to take over her body.
Marlene also makes it clear that this is the Firefly doctor’s theory, and he wants to extract the unique mutation of cordyceps from Ellie’s brain to produce those chemical messengers in a lab to make a cure. This is relatively close to the game’s reasoning, and we find out later just how important the doctor actually is to the future narrative.
Ellie has had the cordyceps since birth because her mother, Anna, was attacked and bitten while in childbirth. Anna does not cut the umbilical cord until after the bite, and so she is infected while still in labor. This allows the cordyceps to enter Ellie’s body and trigger the immune mutation. This event is not directly shown in the game, and so the TV series is how we come into this knowledge.
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The events of the ending to The Last of Us continues into Part II, and Joel’s decision has been debated among fans for over a decade. The game chooses not to necessarily spell out Ellie’s immunity clearly, but the answer granted by HBO doesn’t alter the narrative in any way. It just takes what is there and makes it definitive for fans.
