How to design a plague

James Vaughan designed a game about a virus that itself went viral.

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In 2009, Malcolm Casadaban checked himself into a hospital after contracting the plague in urban Chicago, Illinois.

Casadaban's daughters say the active 60 year-old professor at the University of Chicago was in good health in the period leading up to the illness.

His death 12 hours later rocked a dumbfounded medical community. A professor of molecular genetics, he was researching a chain of events that happens once a person is made sick by a form of plague bacterium called Yersinia Pestis. At some point in his experiments he became exposed to a weakened strain that entered his blood. The university was put into lock-down.

Casadaban died thinking he had the flu. In reality, a series of accidents and a hereditary condition made him one of the few people in recent history to contract a strain of a disease that at one point killed millions throughout the Middle Ages.

It's by coincidence that in creating a virally successful app, British game designer James Vaughan has tapped into one of the greatest global fears. Plague Inc., a strategy game that simulates the spread of modern-day plagues, has become — unintentionally — a model to educate the public on how a pandemic could take rise from just one infected patient.

The incubation period

The iOS bubble has burst, says Vaughan. In the wake of the mobile generation of Angry Birds and Cut the Rope, he explains, developers are delusional if they believe easy success can be found on the App Store.

"Any small developers who aim to make any money from the App Store are a couple of years too late," he says. "Maybe when the iPhone launched then yes, or a couple of years after that a clever person could pull something together that's good and release it. But now the competition you're facing is astounding. What is it, like 400 apps released every day?"

Vaughan talks of the halcyon days of the Killer App with the practical if world-weary tone of a man whose own app, the strategy virus simulator Plague Inc., wasn't already named the most popular paid app currently on the Japanese and Korean market.

In reality the game is an international hit. Not only did Vaughan tap into the very real world of modern pandemics, he also made a video game about viruses that itself went viral.

"I wish I could be able to say that while making a viral game I learned how to make the ultimate viral game from a social point of view," says Vaughan.

But the success of Plague Inc. is undeniably social, the result of word of mouth from player to player. "That aspect of the app is the only reason it's done well," he tells us.

Plague Inc. puts the player in the role of a pathogen. They can choose to be a bacterium, virus or parasite. They must avoid letting humans find a cure. They must avoid detection. They do this by choosing traits that allow them to spread unnoticed until it's too late. Their goal is to kill everyone in the world.

In the context of that universe, it's fitting that the world of viral popularity and epidemiology should overlap. The growth of mobile apps has resulted in its own marketing philosophy and jargon borrowed from a medical field it's tried for years to mimic.

In viral marketing, the "K-factor" is one of the best known formulas to describe just how successfully something can be spread. The term, which originated in epidemiology, is best known for measuring the spread of infection.

The recent trends in iOS sales all point to the difficult, almost impossible task of breaking the market.

For a game like Plague Inc. to make a lucky strike in the app market, it follows the same path modeled by physical viruses. In the now-bastardized formula for the K-factor, the result of the number of links sent by users is multiplied by the percent conversion of every invitation sent. This is used to gauge just how far something can be distributed from person to person, app or disease.

But even today when Vaughan is asked whether he had any idea Plague Inc. would go viral he says, pointedly, "God no." The recent trends in iOS sales all point to the difficult, almost impossible task of breaking the market.

Still, behind the disbelief are hard facts: In its first week of release in 2012, it became the top paid games app in the U.K. Two days later, it hit the U.S. charts in the same top spot. The game has spread to 15 million users, says Vaughan, who adds that the number has likely increased in recent months since being localized for Asian markets.

It's still growing.

James Vaughan

The entrepreneurial bug

Vaughan winning an award at the 2013 Pocket Gamer Awards

Vaughan has just moved into a new office. It's a building based in central London, purchased as a work space for when his small staff of freelancers — programmers and artists currently working and living abroad — comes to England.

As the studio's only local member, Vaughan is for the most part alone in this office. It still means he has to get dressed in the morning, he says. This is the group's first step toward becoming a physical company after years of being an idea.

For Vaughan an idea on its own isn't enough. He refers to a video by comedian Ze Frank. Called Brain Crack, the video describes people afflicted with creative ambitions that never come to fruition.

"It's all about this concept of people who have these ideas and they imagine themselves as becoming so successful and everyone is clapping and their main problem is that they don't have enough hands to carry all of their money," he says. "And they're so focused on this dream world that they never actually do anything."

It resonated with Vaughan.

Plague Inc. is the result of what he refers to as a time when he first caught the entrepreneurial bug, something he hoped to spread among friends looking for inspiration to begin their own independently led projects.

"For me," he says of the video he watched years earlier, "it's a concept of intellectual masturbation when you have an idea in your head and you poke it and you think about how wonderful it would be and it almost numbs you and stops you from doing anything with it."

Vaughan has a posh and practical drawl, a leftover from his former white collar career in consultancy where he advised companies across the U.K. on management and technology. It's a far cry from his new line of work.

"In my spare time I spent about a year creating the game on evenings and weekends," he says. "Management consultancy never quite scratched that entrepreneurial itch. I did it for about four years, straight out of university after I [studied] Economics. But it was always the case that you were a very small cog in a very big machine. You never had the ability to really take control and do things the way you wanted to. As a consultant you're there making recommendations to people."

But Vaughan has no expertise in epidemiology. His degree in economics could now be considered irrelevant in the context of Plague Inc. And yet, it's training that has served him well in his task to scrutinize every step of a disease and transform it into a series of in-game algorithms.

Despite this lack of formal medical knowledge, his game simulates the complexities of outbreaks with enough realism to impress the official CDC. In fact, he was invited to America earlier this year to discuss how he modeled the spread of infectious diseases inside the game.

"I spent months making sure that it worked properly."

"I went with real life," says Vaughan. And likewise, for the CDC the threat of modern global epidemics is very real. Now, in a deeply globalized world, diseases can no longer be dealt with independently between communities. The same can be said of independent developers attempting to forge new careers.

Vaughan's algorithms not only describe the movement of diseases in Plague Inc.; they also express the behavior of its iOS market. Plague Inc. itself is based on a core idea in the science of epidemics called the Basic Reproduction Rate, known under its alternative name as R0 — pronounced R-nought.

In epidemiology, the Basic Reproduction Number of an infection refers to the average number of infection cases generated by a single infected person. This was originally used to construct models of the spread of malaria in the 1950s and more recently was used as a plot point in Steven Soderbergh's film Contagion.

"I spent months making sure that it worked properly," says Vaughan, referring to the algorithms behind that system.

"'R0' asks the question 'How many people can be infected in a given amount of time,'" he explains. "Usually 24 hours. It's pretty simple, but the complexity comes in calculating that number a lot of the time in real science."

When R0 is less than 1 then the infection will die out. Alternatively, if R0 is greater than 1, the infection will spread through an entire population.

"The algorithms and all the tweaking took months and months," Vaughan says. "I started off having all of my algorithms in an Excel spreadsheet and I could map how they're trending and how they interact with different variables. We have thousands of different variables in the game. It takes an enormous amount of time."

Like the K-factor, R0 is adopted in studies of social virality by representing how many times something can spread from a single source. The bigger the value, the harder it is to control in a given population.

"I was on the tube," says Vaughan. "It was a couple of weeks after launch and I was sitting opposite someone playing on their phone. I couldn't see the screen but I was looking at the way he was holding it and the way he was tapping it. I looked at the reflection in the window, and as I was getting off I leant over and it was Plague Inc.. My friends call me every time they see someone playing it on the train or on a plane. They seem to see more people playing it than I do."



For a modern plague to spread several factors need to be in place, Dr. Amesh A. Adalja, adjunct instructor for the division of infectious diseases at the UPCM Centre for Health Security at the University of Pittsburgh Medical Center tells Polygon.

You need a susceptible population. Those infected need to be highly infectious to others in order to continuously spread to new hosts without dying out.

This can be fostered by individuals spreading their infection before their symptoms start to show, in other words "before they know they're sick," says Adalja. This can become magnified by people traveling between regions.

"All of humanity, no matter how rich you are or poor you are or the color of your skin, everyone can get ill."

It took three years after his death before the CDC finally diagnosed the strain of bacterium that killed Malcolm Casadaban as non-threatening at the global level. For Vaughan, it's this above all else that is fundamental to Plague Inc. The game went viral because it is universal.

"The theme of the game translates perfectly across all cultures and because it's based on science," says Vaughan.

"All of humanity, no matter how rich you are or poor you are or the color of your skin, everyone can get ill," he says.

"I think it's hard to think of something that applies so evenly to everybody." Babykayak

Images: James Vaughan, Ndemic Creations, Kris Elliott
Editing: Russ Pitts, Matt Leone

Design / Layout: Warren Schultheis, Matthew Sullivan