The Last of Us creator Neil Druckmann has addressed a long-standing question about the Fireflies’ attempt to develop a cure using Ellie’s immunity. Fans have debated whether the treatment would have succeeded or if Joel’s actions were justified. Druckmann’s answer sheds light on this crucial moment in the story.
Would Ellie’s cure have worked?
In the first season finale, which closely follows the game’s storyline, Joel learns from Marlene that the procedure to create a cure from Ellie’s immunity would be fatal to her. Joel then kills the Fireflies and escapes with Ellie, believing the cure wouldn’t work and that they had to flee due to an attack.
However, Druckmann has confirmed that the Fireflies’ cure would have worked. Speaking on the Sacred Symbols podcast, he explained that the intention behind the story was that the Fireflies could develop a cure for the Cordyceps infection using Ellie’s distinct immunity.
“Could the Fireflies make a cure? Our intent was that, yes, they could,” Druckmann said. “Now, is our science a little shaky that now people are questioning it? Yeah, it was a little shaky and now people are questioning that. I can’t say anything. All I can say is that our intent is that they would have made a cure. That makes it a more interesting philosophical question for what Joel does.”
At the show’s start, Dr. Neuman explains that no treatments or cures exist for the fungal outbreak, setting a grim tone. Over 50 years later, the Fireflies believe they can create a cure, but the lead researcher is killed before completing the work. Druckmann’s confirmation means Joel’s choice to save Ellie over the world becomes a deeply personal and philosophical dilemma rather than a question of scientific feasibility.
Joel’s decision to kill the Fireflies and take Ellie home carries more emotional weight knowing the cure was possible. Ellie’s anger when she discovers Joel’s actions reflects this tension: “I was supposed to die. That was my purpose. My life would have fking mattered, but you took that from me,” she tells him in Episode 6.
The show also explains the science behind Ellie’s immunity. Marlene describes a chemical messenger in Ellie’s body that tricks the Cordyceps fungus into thinking she is infected, making her immune. The Fireflies planned to extract this chemical, multiply it in a lab, and distribute it as a cure.
