The Last of Us finale finally reveals the truth behind Ellie’s immunity to the Cordyceps brain infection that has plagued humanity.
The show’s central plot point, established in episode 1, involves Joel escorting Ellie to the Fireflies due to her immunity from the infection that caused the world’s downfall. The Fireflies believe that if Ellie can be delivered to them, they will be able to create a cure for the Cordyceps infection, enabling her to assist in the restoration of the world from the brink of collapse.
Throughout The Last of Us, Ellie’s immunity has been a prominent feature, but the show has not satisfactorily explained how her immunity is possible. The series has raised doubts about Ellie’s immunity, particularly in episode 7’s heart-wrenching finale, where Ellie receives a bite that shows indications of the Cordyceps fungus being present in her system.
Despite this, Ellie remains unaffected while the rest of humanity succumbs to the infection, prompting questions about her unique ability. However, these questions are finally addressed in episode 9 of The Last of Us, culminating in the conclusion of the first season.
In the beginning of The Last of Us episode 9, a new scene created specifically for HBO’s adaptation unfolds, depicting Anna, Ellie’s mother, fleeing from the infected while in labor. Anna seeks refuge in a remote, deserted house that she believed was occupied by Fireflies.
She barricades herself in an upstairs room, but an infected pursues her and bursts through the door, forcing Anna to battle it off. This scene marks the first appearance of Troy Baker, who played Joel in the game.
During the intense battle, Anna manages to defeat the infected, unaware that the stress of the confrontation triggered the onset of her labor. She gives birth to a baby girl, whom she names Ellie, but only realizes afterward that she was bitten by the infected.
In a quick decision, Anna cuts the umbilical cord that connects her to Ellie. This act leads to Ellie’s immunity in The Last of Us as the Cordyceps fungus present in Anna’s bloodstream is passed onto Ellie through the umbilical cord. Despite this, Marlene clarifies in a later episode that Ellie was not infected.
In the middle of The Last of Us episode 9, Marlene discloses the real reason behind Ellie’s immunity to Joel, which is discovered by the Fireflies’ surgeon. According to the surgeon, the Cordyceps fungus present in Ellie’s system since birth acts as a sort of “chemical messenger.”
This messenger acts as a barrier, fooling any new Cordyceps fungi entering her body – such as the bites she received in The Last of Us episodes 2 and 7 – into thinking that she is already infected. This renders her immune to the effects of the Cordyceps infection.
In The Last of Us episode 9, the disclosure of Ellie’s immunity leads to speculation about the possibility of finding a cure. According to Marlene, the surgeon planned to extract the Cordyceps present in Ellie since birth and replicate the cells, resulting in more of these “chemical messengers.”
The surgeon believed that this could produce a cure by injecting the chemical messengers generated by Ellie’s body into the rest of the population, as explained to Joel by Marlene.
In The Last of Us season 1, episode 9, Joel’s actions render the possibility of the Fireflies creating a cure irrelevant since the only surgeon who could have possibly done so is dead.
Throughout the episode, there are indications both for and against the possibility of a cure. Marlene’s choice of words is noteworthy when she tells Joel that the surgeon “thinks” Ellie’s condition could be a cure. The use of the word “thinks” implies that the surgeon is not entirely certain about the cure’s feasibility, only that he believes it might be possible.
In the final moments of The Last of Us episode 9, Joel lies to Ellie about the possibility of other immune people existing, despite her being the only known case. This means that even if the surgeon is not entirely sure of creating a cure, he would still try due to the significance of Ellie’s immunity.
Whether a cure is possible or not, both the game and TV adaptation of The Last of Us do not provide a clear answer. Ultimately, the focus of the episode is on Joel’s decision and the complexity surrounding it.
About The Last Of Us
The Last of Us is an HBO TV series adaptation of the award-winning video game of the same name originally developed by Naughty Dog.
It is set in 2033, as a fungal infestation plagues humans, turning them feral and blind before finally finishing them off. The series follows Joel’s journey to escort an immune 14-year-old Ellie to the Fireflies, who hope to study her to procure a vaccine.
The cast comprises Pedro Pascal and Bella Ramsey, both famed for their roles in Games of Thrones, along with Gabriel Luna, Merle Dandridge, and Nico Parker. The show was renewed for season 2.