How to design a plague

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 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."