The Last of Us 2 has been out for a couple of weeks now, and while the game received positive reviews from critics, some fans were not happy with Naughty Dog's follow up on the iconic 2013 game. Despite retaining the immersive gameplay, a detailed world, and a deep narrative that Naughty Dog is known for, fans of the first game heavily criticized the sequel, especially when it comes to the fate of the game's primary characters. Note: MAJOR SPOILERS follow.

However, putting all the plot twists aside, one important storyline in The Last of Us 2 revolves around Ellie's immunity and the possibility of developing a vaccine for the Cordyceps infection. In the first game, it was revealed that The Fireflies were planning to conduct a surgery on Ellie to remove a mutated form of the Cordyceps and reverse-engineer a vaccine. However, given Joel's intervention that led to the death of the surgeon, the operation that was supposed to extract a vaccine out of Ellie's immunity never came to fruition. But if Joel never intervened, would the surgery be a success? Was there really a vaccine that could have ended the Cordyceps infection?

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It Appears That There is a Vaccine, But There's a Catch

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During a flashback scene in The Last of Us 2, players saw Ellie return to the hospital where Joel saved her from The Fireflies in search of answers. For those who haven't played or may have forgotten the events of the first game, Joel and an unconscious Ellie were able to escape the hospital. Towards the end of the game, Joel lied to Ellie saying that The Fireflies conducted tests on her and discovered that her immunity meant nothing. Although Ellie reluctantly accepted Joel's answer, it is obvious that she was skeptical of his explanation. Back to the flashback scene in The Last of Us 2, Ellie explored the hospital where she was supposed to undergo surgery in hopes of developing a vaccine. Notes scattered around the hospital suggested that The Fireflies were optimistic that the surgery would yield a successful result.

However, Ellie also found a recording made by an unknown member of The Fireflies after Joel rescued Ellie and left the hospital. The recording revealed that because Joel killed the surgeon that was supposed to perform the operation, there is no more hope in developing a vaccine even if they find other immune people, given that this particular surgeon is the only one who knows how to reverse-engineer a vaccine out of the mutated Cordyceps infection found in Ellie's brain. Although the game never guaranteed that the surgery would be 100% success, the pieces of evidence that Ellie found upon returning to the hospital suggests that the chances are high. But the question now is, had Joel's rescue failed, and The Fireflies were able to make a vaccine from Ellie's immunity, how will they produce it? And will they use it for the common good?

How Would The Fireflies Mass Produce the Vaccine?

One thing that the current real-world coronavirus pandemic tells us is that a vaccine is not easy to make. Even if scientists were able to make a successful strain that could produce immunity to some people, it may not work for everyone, which is why a vaccine for COVID-19 and other diseases, is still non-existent. Additionally, even if The Fireflies were able to make a working strain that would work for everyone out of Ellie's immunity, how will they mass produce it given the dilapidated state of the world they are living in? To successfully mass-produce the vaccine, it would take an enormous amount of resources and medical equipment, which is something that The Fireflies do not have.

Additionally, if The Fireflies were able to mass-produce the vaccine, will people accept it? In The Last of Us 2, it has been revealed that humanity has since been divided into numerous factions, and most of those factions are at war with one another. Given the fall of a centralized government, many people took advantage of the lack of stability to establish groups in hopes of dominating what is left of the world, and The Fireflies is one of them. Although The Fireflies may have good intentions, who's to say that they wouldn't use the vaccine as some sort of leverage to increase their power and influence over other survivors?

In the end, while Ellie's immunity could have allowed The Fireflies to create a vaccine, it does not guarantee that the world they are living in would return to normal given the lack of resources and the high chance of corruption within the organization. Although it wasn't shown in the game, it is possible that Joel may have also thought of these scenarios, which is why he refused to sacrifice Ellie for The Fireflies' unrealistic ambition.

The Last of Us 2 is out now exclusively for the PlayStation 4.

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