What Are the Different Stages of Infection in The Last of Us? Cordyceps Infection Explained


We all know that the main reason for the apocalypse in The Last of Us is the Cordyceps Brain Infection (CBI), which forced humans to become mindless monsters that attacked other people. This led to the fall of human society as civilization never recovered well enough in the two decades that followed the outbreak of the CBI. Those who are afflicted by this infection have almost no chance of recovering, and that’s why it is more dangerous than any other outbreak we’ve seen in post-apocalyptic storylines.

However, the thing about the CBI is that it has different stages of infection, depending on how long the person has been exposed to it. The higher the stage of the infection, the more monstrous the person gets. So, with that said, we are here to look at the different stages that a person undergoes when he has been infected by Cordyceps.

What Is The Cordyceps Brain Infection?

While we do know that the world where The Last of Us takes place has fallen due and is now a shell of its former self where people have to fight one another to survive, we also know that the reason why the entire planet has gone to hell is an outbreak that turned people into mindless monsters that attacked other people. The cause of this outbreak is the Cordyceps Brain Infection (CBI). So, what exactly is the Cordyceps Brain Infection?

We’ve seen in a lot of different post-apocalyptic movies, shows, and games how the entire world went to hell due to a zombie virus that could spread from one person to another through a bite. However, the thing about the CBI is that while it works the same and has similar effects, its nature is quite different. And the scary part is that it is actually something that happens in nature.

In the natural world, Cordyceps is a type of fungus that can infect insects through spores that spread from other infected insects as well. These spores can grow as fungi that can take over the mind of the insect and feed off of its body. In return, the fungus controls the host insect and keeps it alive long enough for the infection to grow and produce more spores that could spread to other insects.

Cordyceps are dangerous in the insect world because how they can cause the destruction of an entire colony if one insect gets infected. This fungus mostly affects ants but can also affect other insects. The ants that are infected by Cordyceps tend to act differently and violently compared to the other ants.

The good news is that, in the real world, Cordyceps has no effect on any other creature aside from insects. But The Last of Us found a way to use this concept such that the fungus has evolved to affect human beings as well. As such, when humans are exposed to the spores of the Cordyceps or are bitten by those who are infected by it, they will also get infected.


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Once infected, a human being would show signs and symptoms in a matter of a few hours or even a few days. It depends on the person’s body and on the extent of the infection. But the point is that an infected person is going to get their mind taken over by the Cordyceps fungus.

The fact that CBI is a fungal infection means that there is no vaccine or medicine for it. It is unlike the viral zombie infections that we see in movies, shows, and games, as viruses tend to have medicine or vaccines. Of course, another thing that makes the CBI unique is that it only affects live hosts as opposed to turning dead people into the undead.

What Are The Different Stages Of Cordyceps Infection?

The thing about the CBI is that once it infects a person, the host goes through different stages of infection depending on how long they have been infected. Of course, it only takes a few hours to two days for the person to lose their mind to the infection, but it would take a while for the infection to force the person’s body to undergo rapid changes and mutation. So, with that said, here are the different stages of Cordyceps infection found in The Last of Us game and probably even HBO’s version.


Runners are the people who were recently infected and have lost their minds to the infection. That means that it has only been a while since they were infected. They are the most human-like in terms of their features, as the fungus is yet to transform their bodies.

As suggested by what they are called, Runners are the fastest in terms of how they run. Nevertheless, they are quite sluggish in their attacks. Still, they more than make up for their sluggishness by attacking in hordes, as the fungus has a way of communicating with an entire horde of infected.


Stalkers are people who have been infected longer than Runners have. It usually takes two weeks to a year for an infected to stay in the Stalker stage. And the thing about them is that they are quite unique in terms of their behavior.


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Unlike Runners, which actively seek out their prey, Stalkers tend to stalk their prey in the dark as they usually only attack when they have a chance to do so. That’s why Stalkers are mostly found in dark places like abandoned buildings, as they can ambush people by hiding in the dark. There are also Stalkers that latch onto walls to allow the fungus to fester so that the Cordyceps can keep the host alive long enough for the Stalker to ambush prey.


Clickers are some of the scariest infected in terms of their appearance, as their heads are mushroom-like already. They hardly resemble regular humans due to how advanced the infection has become. In most cases, infected people turn into Clickers if they have been infected for at least a year already.

In that regard, the fungus has already spread throughout the entire body of the host, as the fungus has already blinded the person. This forces the Clicker to use echolocation to find prey. Clickers are also so much stronger than regular people, and that’s why they are fearsome whenever they force their prey into close-combat situations.


Bloaters are infected people that have been infected for years already, as this is the stage where the infected is at its strongest in terms of physical strength and durability. The fungus has already taken over the entire body and has grown into armor-plating that protects the host’s body. While Bloaters are slower than Clickers, they are far stronger and more durable.

Due to their immense size, strength, and durability, Bloaters tend to be problems even for experienced soldiers. What’s scarier is that they have the ability to tear fungus from their bodies to use them as spore bombs that could spread the infection faster. But the problem is that Bloaters are more vulnerable to fire due to the additional fungal growth in their bodies.


If you think that Bloaters are scary, Shamblers are scarier as these are people who are already so advanced in the infection stage that they have transformed into terrifying creatures that can grapple prey and expel large spore clouds from their bodies to spread the infection faster. They are not as common as the other stages of infection due to the fact that Shamblers are often found in places with plenty of water.


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Shamblers aren’t as physically enhanced as Bloaters and Clickers, and that’s why they aren’t as strong in terms of their physical strength. Nevertheless, a dead Shambler would release a cloud of Cordyceps spores into the air, making them scary enemies to face for any experienced fighter or soldier.

Rat King

The Rat King is a unique stage of infection that only happened in the Seattle hospital after a person had been infected for more than 20 years already. In fact, this is an anomaly that is composed of several infected combining into one to create an infected that is colossal in terms of size and strength.

It is the very fact that the Rat King is so huge and is composed of several infected that makes it durable enough to withstand damage from guns, bombs, and fire. And even after death, the Rat King will simply allow the different infected to break off from the larger mass.

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