The Simian Flu is one of the most important story elements in the modern Planet of the Apes series, and here’s everything that there is to know about the disease, including its origin, effects, and more. Starting with Matt Reeves’ Rise of the Planet of the Apes, the modern Planet of the Apes reboot series looked at the franchise through a new lens, exploring how the hyper-intelligent apes actually managed to overthrow Earth. In the lore of the franchise, the Simian Flu is key to this historical change, and here’s how it came to be in Planet of the Apes.

The Planet of the Apes franchise is one of the most beloved sci-fi series of all time, with it exploring all kinds of different concepts and ideas by means of a world run by apes. While the original 1968 film explored a society of already-evolved apes, Matt Reeves’ Planet of the Apes trilogy instead decided to tell the stories of how these evolved apes came to be. Reeves’ trilogy tells the saga of Caesar, but the series didn’t die with the beloved ape, as it is returning soon with Kingdom of the Planet of the Apes.

Gen-Sys Laboratories Created The Simian Flu In Planet Of The Apes

As Seen In Rise Of The Planet Of The Apes

The story of the Simian Flu starts in Rise of the Planet of the Apes at the fictional company Gen-Sys Laboratories. James Franco’s Dr. Will Rodman was attempting to develop a cure for Alzheimer’s known as ALZ-112, with it advancing to the stage of testing the drug on chimpanzees. ALZ-112 worked on a test subject named Bright Eyes, but the ape became aggressive and attacked some of the lab’s employees, causing security to kill her. Funding for the project was cut, but Rodman stole the remaining samples of ALZ-112 and took them home to test on his father.

Rodman eventually desired to make a stronger variant of the vaccine, leading to the development of ALZ-113. While this strain gave apes increased intelligence, it was fatal to humans. An ape escape incident caused a human to become infected with ALZ-113, with him passing it on before dying. After this event, ALZ-113 spread throughout the human population like wildfire, going overseas and infecting humans on every continent. The outbreak was eventually nicknamed the Simian Flu Pandemic, with the title coming from the virus’ ape origins.

The Simian Flu Killed 99% Of Humanity After Rise Of The Planet Of The Apes

Devastating The Population

The Simian Flu proved fatal to most humans, with it killing 99% of humanity after the events of Rise of the Planet of the Apes. The human population was decimated in a short period of time, leading to societal collapse. While the Simian Flu killed most humans, it didn’t kill all of them. About 1% of the human population was immune to the Simian Flu, with their immune systems not being compromised by the virus. These humans are still carriers of the Simian Flu, but the virus turned out to not be fatal to the survivors.

While humans were susceptible to the Simian Flu, the virus actually helped the ape population immensely, causing apes to quickly overpower human society. Due to the original intent of the virus, the Simian Flu generates cells in the brains of apes, causing them to be stronger and more intelligent. However, the comparatively weak immune systems of humans caused them to be susceptible to the Simian Flu, leading to the mass death event after Rise of the Planet of the Apes.

The Simian Flu Created Evolves Apes Around The World

It Wasn’t Just Caesar

Caesar and the apes originally exposed to the drug aren’t the only apes that were evolved, as the Simian Flu caused a permanent shift in apekind. Any child of an ape infected with the Simian Flu can also become evolved, meaning that after only a couple of generations, the entirety of the ape population was more evolved. By the time Kingdom of the Planet of the Apes rolls around, nearly every ape on Earth is more evolved than they were before Rise of the Planet of the Apes.

The Simian Flu Mutated After Dawn Of The Planet Of The Apes

Things Got Worse For Humans

Although it seemed impossible, things actually got worse for humanity after Dawn of the Planet of the Apes. As is explained in War for the Planet of the Apes, the Simian Flu actually mutated once again, further affecting the 1% of the population that didn’t die during the initial pandemic. Rather than killing the infected, the mutated strain of the Simian Flu causes humans to lose their ability to speak and become feral, turning them far more violent than they otherwise would be.

The new Simian Flu can spread through direct contact, but it also remains on surfaces that the infected have made contact with, such as Nova’s doll. This means that human civilization was demolished even further, as the once-immune humans quickly became subject to infection.

How Humanity Survived The Simian Flu Until Kingdom Of The Planet Of The Apes

They Are Now Feral

Although the evolved Simian Flu in War for the Planet of the Apes has an effect on the once-immune humans, this new strain isn’t deadly. Instead, it regresses the humans into a feral state, one in which they lose their ability to talk and devolve into their most basic instincts. This allows some form of humanity to survive until Kingdom of the Planet of the Apes, where the apes have taken many humans as slaves. This goes to show how far humanity has fallen since the start of the modern Planet of the Apes trilogy.