The Last of Us: 8 biggest changes from the video game in season 1

7. Ellie’s mom and the explanation of Ellie’s immunity

The fact that Ellie is immune to the cordyceps fungus is the lynchpin of the story; everything else revolves around that potentially world-altering fact. However, in the game, we never find out exactly why Ellie is immune. Sometimes in nature things just happen, and explanations are hard to come by.

The show takes a different route, revealing in the season finale that Ellie’s mother Anna (played by Ashley Johnson, the same actor who portrayed Ellie in the games) was bitten by an infected during childbirth. Anna quickly cuts baby Ellie’s umbilical cord, but by then she had enough of the cordyceps is in her system to change her biology. We later discover that it’s this baseline amount of cordyceps which fools the fungus into thinking that Ellie is already infected, preventing it from spreading and taking over her body.

None of this is ever explained in detail in the game. We only ever learn about how Marlene and Ellie’s mom knew each other very briefly at the end of the game. Their relationship is expanded upon in the tie-in comic The Last of Us: American Dreams.

Of all the changes the show has made, the decision to explain Ellie’s cordyceps immunity is the one which could become the most important moving forward.  Who knows how it could tie into The Last of Us season 2?