The Last of Us Episode 9 certainly delivered a powerful conclusion for the show's first season. In addition to revealing that Joel had tried (and failed) to kill himself after the death of his daughter, Look For The Light finally offered an amazing explanation for Ellie's immunity and it has a lot to do with the terrifying circumstances surrounding her birth.
In The Last of Us Episode 9, it was revealed that Ellie's mother Anna was bitten by an Infected just as she is giving birth. Although Anna quickly severed the umbilical cord, there is a possibility that her body still passed some of the infection to the baby.
Anna insists to Marlene that she was bitten after giving birth but Marlene later explains to Joel that she realized that the baby was somehow infected. Marlene tells Joel that the cordyceps in Ellie's body grew with her since birth and it produces a chemical messenger that warns other cordyceps that she is also cordyceps thus making her immune.
It's an amazing explanation for Ellie's immunity and it wouldn't have been possible if she was born in a safe environment. It is also awesome to know considering that the game never explained the reason why Ellie is immune. With that in mind, this is one divergence from the Naughty Dog game that was truly welcome.
Ellie's immunity also makes her the perfect donor for a possible cure. However, Joel decided that he didn't want the girl to sacrifice her own life for the rest of the world. This decision, and his lies about what truly happened at the hospital, could potentially shake things up between him and Ellie in The Last of Us Season 2.
All episodes of the first season of The Last of Us are now streaming on HBO Max. The Last of Us Season 2 has already been confirmed and is expected to begin filming soon.
Related: The Last of Us Episode 9 Concludes With Joel's Game-Changing Decision