The Last of Us season 1 finale finally explains how Ellie is immune

We’ve made it to the conclusion of The Last of Us season 1, and I think people will be talking about this finale for a long time to come. It’s action-packed, gut-wrenching, and ends on an uneasy note that’s difficult to process. Creators Neil Druckmann and Craig Mazin have made a damn good show.

Episode 9, titled “Look for the Light,” sees Joel (Pedro Pascal) and Ellie (Bella Ramsey) finally getting to their destination and reuniting with the Fireflies, but things don’t go as expected. Far from it, actually. Joel and Ellie’s relationship has developed so much since the first episode, and we can really see how integral Ellie has become to Joel’s life by the finale.

Warning: There are major SPOILERS ahead for The Last of Us Episode 9.

Apart from seeing how far Joel will go to keep Ellie safe, we also learn something in the season 1 finale that we’ve been wondering about this whole time.

The opening scene in Episode 9 follows a pregnant woman going into labor while running away from infected; she ends up giving birth before being attacked. We learn that this is a flashback scene of Ellie’s mom Anna, who’s played by the original Ellie voice actor from The Last of Us video game, Ashley Johnson. So of course, that means the baby is Ellie. Anna is bitten before she’s able to cut the umbilical cord, which would seem like it’d spell danger for Ellie, but it actually does the opposite.

Eventually, Marlene gets to the house and sees what happened. Anna tells her that she was attacked after she cut the umbilical cord, which isn’t true. Because of this, Marlene agrees to keep Ellie safe, and is then forced to shoot Anna before she turns.

How is Ellie immune in The Last of Us?

It’s implied from this scene that Ellie is immune to the fungus because of the attack her mother suffered, and by the end of the episode, what Marlene tells Joel kind of confirms it. She explains to him that their doctor believes the cordyceps in Ellie have been growing inside of her since she was born, which again implies she was infected when her mom was attacked. But probably because she wasn’t the one bitten, the cordyceps that infected her actually worked as an immunity, not a disease.

Marlene says the infection inside of Ellie produces chemicals that tell normal cordyceps that she’s cordyceps, which is why her body isn’t affected by bites or attacks. After coming to this conclusion, the Fireflies decide the best course of action would be to perform surgery on Ellie to remove the cordyceps and multiply the cells in order to create a vaccine. This, of course, would change the world, but it also means Ellie would probably die because cordyceps live in the brain. And Joel won’t accept that.

The most shocking part of The Last of Us season 1 finale comes soon after this conversation when Joel decides to kill all of the Fireflies to save Ellie. What makes his decision all the more heartbreaking is that once Ellie wakes up, he lies to her about the whole thing. This will make their relationship more complex in the second season, especially because the final moments in the episode suggest Ellie might not actually believe him.

All nine episodes of The Last of Us season 1 are now streaming on HBO Max.

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