Why is Ellie immune in The Last of Us? Episode 9 explains all

Pedro Pascal (Joel) and Bella Ramsey (Ellie) delivered career-best performances throughout the series, based on the wildly popular games, with the show providing a shocker of an ending.

However, one of the earlier scenes, starring Ashley Johnson, who voiced Ellie in the games, provided some answers to a question that has been bugging fans all season - why exactly is she immune?

We've seen lots of Ellie's backstory, including her beginnings at FEDRA school, her close bond with Storm Reid's Riley, and some of the tragedies that have made her so tough.

But, with the introduction of Johnson as Ellie's mum, we learnt a lot more.

Why is Ellie immune in The Last of Us?

Throughout the series, it's made clear that Ellie - and seemingly Ellie alone - is immune to cordyceps.

We find out in episode 7 that she was bitten during her night-time outing with Riley and watched her closest friend "lose her mind" while nothing happened to her. But in episode 9, we find out why.

The episode opens with a heavily pregnant woman, who is later revealed to be Anna, Ellie's mum, fleeing from infected before being forced to give birth alone in an abandoned building.

Marlene (Merle Dandridge) finds her hours later - with a dead infected by her feet, as Anna reveals she's been bitten. When she was bitten, Ellie was still briefly attached to her mother, before Anna cut the umbilical cord, meaning the cordyceps has been with her since birth.

It's this immunity that made doctors believe that Ellie could be the key to a cure.

Marlene explains to Joel in episode 9 that Ellie's body creates "chemical messengers" that made the cordyceps believe that she was part of the infected already, and it didn't take control of her body as it did with everyone else.

Is anyone else immune?

During the finale episode, Marlene claims that no one else is immune.

However, the process of Ellie becoming immune raises an important question - if another pregnant person is bitten, would this also make the baby immune?

Only time will tell as to how the story continues, but, after Joel's rampage through the hospital, for now it seems as though humanity's only hope for a cure is lost.

The Last of Us is exclusively available on Sky Atlantic and streaming service NOW – find out more about how to sign up for Sky TV.

Check out more of our Sci-Fi coverage or visit our TV Guide and Streaming Guide to find out what's on this week.

Try Radio Times magazine today and get 12 issues for only £1 with delivery to your home – subscribe now. For more from the biggest stars in TV, listen to The Radio Times Podcast.