The end of The Last of Us Episode 1 brings a big reveal regarding Ellie's character that can be confusing to anyone unfamiliar with the game.
Warning! spoilers for both the first episode of HBO's The Last of Us and the original game.
The first episode of HBO's The Last of Us revealed an important component of Ellie's character, and here's everything you need to know about the reveal in question. The Last of Us takes place in two different places in the world's timeline. The show begins with an introduction to the infection that will decimate humanity, where two scientists present their views on the greatest threat to humanity, one of which says that fungal infections can be more dangerous than bacteria or viruses. The show then picks up in 2003, with Joel, Tommy, and Sarah witnessing an outbreak of Cordyceps infection first-hand. The show then cuts to 20 years later to the year 2023 after everything has gone to mankind.
The Last of Us shows the post-apocalyptic life of the Boston Quarantine District through the eyes of Joel (Pedro Pascal) and Tess (Anna Torv), who are introduced to Ellie (Bella Ramsey) - a girl they're assigned to smuggle out from QZ to the Fireflies for unspecified reasons. Ellie is highly regarded by Marilyn, prompting Joel and Tess to agree to accompany Ellie in exchange for a truck that they can use to search for Joel's brother Tommy. However, the final sequence of The Last of Us episode 1 shows why Ellie is so important to the Fireflies, and why they want to keep her alive at all costs.
Explaining Ellie's immunity
The revelation is that Ellie has some form of immunity to the disease Cordyceps. At the end of The Last of Us episode 1, Joel, Tess, and Ellie are caught by a FEDRA agent outside the Boston quarantine zone who scans them for infection, an important scene taken from The Last of Us. Upon scanning Ellie, she turns and stabs the worker in the leg, causing Joel to have to kill him. Then Tess finds the scanner, which reads that Ellie is infected. After a brief moment of panic, Ellie reveals the stinger is on her arm and that she had had it over three weeks ago. Most infected people in The Last of Us universe begin to mutate within 24-48 hours of being bitten, proving Ellie's immunity.
However, when showing her arm, the bite infection is seen running through Ellie's forearm, which means that the Cordyceps fungus is still present in her system. However, given how she's been "infected" for over three weeks, that means the infection doesn't affect her the same way it affects other humans in The Last of Us on HBO. The main symptoms of cordyceps infection are that it makes people lose higher brain functions, become capricious, and only drive to spread the infection. Ellie, however, has some sort of immunity to this, while not harming her as it does the rest of humanity.
Why Ellie is important to fireflies
This explains why Ellie is so important to the fireflies. Given how the world has been in shambles for over 20 years, and humanity has been wiped out completely with any remaining pockets confined to QZs like Boston, the Fireflies see Ellie as a potential way to return humanity to the way it was. With Eli's immunity, the fireflies hope to manufacture a cure for Cordyceps brain infection. This explains why Marilyn, the Boston Fireflies captain and Last of Us character from the game, was so careful with Ellie by making sure she didn't turn around for a few weeks after being bitten.
Then Marilyn and her team prepare to drop their fight against FEDRA in the Boston area and take Ellie to the Massachusetts State House. There, the Fireflies they were going to meet would likely take Ellie to their base to run tests on her and reveal the cause of her immunity. One of the things that The Last of Us episode 1 establishes, with Tess and Joel surprising Ellie's immunity, is that it's not uncommon. Having someone as rare as Ellie on their hands naturally leads them to seek a remedy to avoid The Last of Us infections and clicks from becoming more common.
How did Ellie become "immune"?
As of the end of The Last of Us episode 1, it is unclear how Ellie became immune to Cordyceps disease. However, some theories have spawned from the game of the same name, on which The Last of Us is based. One of these theories ties to the inclusion of Ashley Johnson in HBO's The Last of Us. Johnson was the original voice actor and mocap performer for Ellie in both The Last of Us Part I and The Last of Us Part II and was confirmed to have a role in HBO's adaptation alongside Troy Baker, who played Joel in the games.
In the trailer for The Last of Us, Johnson and Baker's roles are revealed, with the former hinting at Ellie's invulnerability through a long-running game theory. This theory is that Ellie's mother became infected when she was pregnant with her, which means Ellie was exposed to the Cordyceps infection as a fetus. This could mean that her immunity was instilled in her before she was born, and so when she was later exposed to the Cordyceps infection through the bite, it had no effect on her. This ties in with Johnson, as many assumed she would play Ellie's mother in The Last of Us.
In the trailer, Johnson can be seen holding a newborn baby, with the trailer heavily implying that Johnson's character has just given birth to the infant. Johnson playing Ellie's mother in HBO's video game Last of Us would make sense, as he's a neat tie-in to Johnson's original character in the game and would establish Ellie's early life, which she wasn't focused on in the game. This sequence could confirm that Anna, Ellie's mother, contracted the infection during her pregnancy, which in turn caused her immunity.
Although this has not been officially confirmed in the game, it would make more sense than a simple mutation in Ellie's cells to fend off infection. One clear thing is that the first episode of The Last of Us established Ellie's immunity. Moving on to the rest of The Last of Us, it'll be interesting to see how deep HBO's adaptation of the best-selling game goes at this point, and whether it officially confirms Ellie's immunity to the infection that devastated humanity.
"The Last of Us comes out every Sunday on HBO"