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The Last Of Us Episode 9 Teases The Origin Of Ellie's Immunity

Contains spoilers for "The Last of Us" Season 1, Episode 9 — "Look for the Light"

"The Last of Us" has finally wrapped up its critically acclaimed premiere season, showing audiences the lengths to which people will go to survive in the zombie apocalypse. Granted that Neil Druckmann, the creative director of both video games, joined Craig Mazin as co-showrunner, it's no surprise that they figured out the secret of the perfect video game adaptation.

The season finale includes all the significant moments from the game's final act that fans have been waiting to see: Joel (Pedro Pascal) and Ellie (Bella Ramsey) safely arrive in Salt Lake City, looking for the Fireflies' hospital base; they encounter the famous giraffes from the video game before the Fireflies ambush them; and once at the hospital, Marlene (Merle Dandridge) tells Joel that Ellie will have to die for them to develop a cure for the Cordyceps infection, prompting him to massacre everyone in the base in order to save her.

But while the show masterfully hits all the major beats from the video game, it doesn't get enough credit for taking the source material and elevating it to new heights. For example, Bill (Nick Offerman) was a significant character in the game, but he didn't have nearly as much development as his live-action counterpart, whose episode had fans drowning in emotions from start to finish. Episode 9 continues this trend, taking its time to show the origins of Ellie's immunity, which there wasn't room for in the game.

Druckmann finally gets to show how Ellie became immune

Similar to the HBO series, the game introduces Ellie, with Joel and Tess later finding out she's immune, but there's never a direct explanation of how she became this way. During the winter portion of the game, players can choose to read a letter left by Ellie's mother, Anna, which pretty much just says that she died shortly after giving birth. This led players to believe she got infected while carrying Ellie, which could have resulted in the baby developing natural immunity to the fungus.

Although fans had to wait until the end of the season, the backstory finally gets its time to shine, opening the season finale with Anna (Ashley Johnson) running to an abandoned house to escape an Infected. She manages to kill it, giving birth in the process, but not before it takes a bite out of her thigh. Later in the episode, Marlene tells Joel that the Fireflies' doctor believes the fungus has grown within Ellie since birth, resulting in her immunity and giving fans an answer to the unsolved question.

In an interview with Variety, Neil Druckmann stated that after Naughty Dog released "The Last of Us," he had written a short story about Ellie's mom and planned to develop it into either an animated short or a DLC, but that never happened. Thankfully, the HBO series finally allowed him to explore Ellie's birth, giving the character's voice actor, Ashley Johnson, the spotlight to show how she became immune.