Why is Ellie Immune in The Last of Us?

You may be immune from the infection, but you're not immune from tearing you apart...

by Matthew Kevin Mitchell

Are you wondering why Ellie is immune in The Last of Us? There are a lot of burning questions about this fact, like how and when she became immune to the Cordyceps infection and whether she is the only one in the world that possesses this immunity. However, the show has barely scratched the surface of how important Ellie is to the world. We saw a vital character meet their untimely demise to save Ellie. This character also convinced Joel of the importance of continuing west with Ellie.

The show hasn’t explained it yet, but Ellie being immune could be the key to a vaccine against the infection, which could save what’s left of the world. So then, what do we know about her immunity? Here is everything you need to know about why Ellie is immune in The Last of Us.

Why is Ellie Immune in The Last of Us?


A fan theory that has gained a lot of popularity is that Ellie’s mom, Anna, left her a note when she was only a day old, which states she is dying. The theory goes that Anna was infected before Ellie was born, and her exposure to the infection while still in the womb led to her immunity. This has been highly disputed and still not confirmed as the correct answer. However, in the epilogue of the game, you can locate a surgeon’s recorder that provides an answer to the question, albeit an unsatisfying one. The recorder states:

April 28th. Marlene was right. The girl’s infection is like nothing I’ve ever seen. The cause of her immunity is uncertain. As we’ve seen in all past cases, the antigenic titers of the patient’s Cordyceps remain high in both the serum and the cerebrospinal fluid. Blood cultures taken from the patient rapidly grow Cordyceps in fungal-media in the lab… however white blood cell lines, including percentages and absolute-counts, are completely normal. There is no elevation of pro-inflammatory cytokines, and an MRI of the brain shows no evidence of fungal-growth in the limbic regions, which would normally accompany the prodrome of aggression in infected patients. We must find a way to replicate this state under laboratory conditions. We’re about to hit a milestone in human history equal to the discovery of penicillin. After years of wandering in circles, we’re about to come home, make a difference, and bring the human race back into control of its own destiny. All of our sacrifices and the hundreds of men and women who’ve bled for this cause, or worse, will not be in vain. 

So the answer, according to the recording, is that there is currently no explanation for her immunity. The recording also makes it seem like Ellie is the only one with this immunity (or at least the ones the Fireflies have experimented on). This adds some context and severity to the final words of the character who sacrificed themselves in episode 2 of the HBO series. So, we still have burning questions. How and when did she become immune, and why is she the only one? We won’t know the answer to this question, at least not yet.

Neil Druckmann from Naughty Dog told Newsweek that he had written a story about Anna that became a thing and had been sitting on a shelf all this time. The new HBO series is a perfect platform for this story, and that is the plan. We will see Ellie’s mom in the show, which should provide further insight into why she is immune. Ashley Johnson, the voice actor for Ellie in the games, will play Anna on the HBO series.

The Last of Us will have new episodes released weekly exclusively on HBO.

- This article was updated on January 24th, 2023

Trending on AOTF