A new disease emerged from a remote part of the world. It started in an animal before jumping to humans. It was highly contagious, but many who caught the disease remained asymptomatic. Consequently, when a few travelers became infected, the sickness spread to other parts of the world before anyone knew there was a problem. In an incredibly short span of time, the world went from having never heard of the disease to an unprecedented worldwide pandemic.

Does this scenario sound familiar? If you think this is a description of COVID-19, think again. These events took place 15 years before the eyes of the world focused on Wuhan, China. If you don’t remember the events of that time, it may be because you don’t spend much time playing video games. The Corrupted Blood Pandemic of 2005 played out entirely online, but the experience gained and the lessons learned from the incident helping epidemiologists understand the current world crisis.

World of Warcraft (WoW) is the largest online role-playing game in the world. Known as a massive multiplayer online role-playing game (MMORPG)WoW allows hundreds of thousands of players to interact with the world and each other at the same time.

Launched in 2004, WoW has over 100 million registered accounts and has generated more than $10 billion in revenue, making it one of the highest-grossing video games of all time.

Players in WoW create an online character and team up through alliances known as guilds. Guilds consist of anywhere from 50 to hundreds of players. Together, they participate in challenges called raids.

Hakkar of Zul’Gurub.

On September 13, 2005, a game update introduced a new dungeon area called Zul’Gurub. Zul’Gurub was under the control of a powerful blue-haired winged dragon named Hakkar. Not only was Hakkar very powerful, but he was also a carrier of a disease called Corrupted Blood. Players who came into contact with the dragon became infected with Corrupted Blood, which was intended to weaken the player for about 10 seconds before running its course.

A programming error caused Corrupted Blood to remain in the infected player for much longer than the intended 10 seconds. In fact, it never left. When players left Zul’Gurub, they took the infection with them, spreading it to anyone with whom they came into close contact.

The infection also spread to the players’ online pets. They, in turn, spread the sickness to even more players and animals. The infected players and animals also spread the disease to non-playable characters (NPG), who further accelerated its spread. Within hours, entire cities were overrun with Corrupted Blood.

One week after the pandemic started, the game’s owner, Blizzard Entertainment, had to restart all of its servers to stop Corrupted Blood in its tracks. It is difficult to accurately count the number of players who ended up being infected. Some estimates place the infections at more than 4 million players.

Although the WoW pandemic was able to be controlled through a means that would not work in the real world, epidemiologists realized there were lessons to be learned that might help combat something much more serious than Corrupted Blood. In a paper published in the September 1, 2007, issue of The Lancet Infectious Diseases, researchers Eric T. Lofgren and Nina H. Fefferman reported their findings from studying the spread of Corrupted Blood through social interactions in WoW. Fefferman says the incident has helped inform her current research into predictive modeling around COVID-19.

The researchers noted the similarities between Corrupted Blood and highly-infectious real-world diseases. In an eerie foreshadowing of the COVID-19 pandemic that would come fifteen years later, Corrupted Blood started in an animal in a remote part of the world. With both animal and human hosts — many of whom were asymptomatic — the disease spread to urban areas where it then exploded.

When the disease was first discovered, Blizzard Entertainment took steps to try to control the spread of the disease. It issued statements to players, asking them not to summon infected pets in crowded areas, and to leave the city areas if they were infected. When this didn’t work, Blizzard announced a quarantine, where infected players were told to practice social distancing by avoiding other players and NPCs. Many players refused to cooperate, however.

The researchers also saw a real-world similarity in the unintended spread of the disease through first responders. In WoW, some players have healing abilities. Many of them attempted to offset the spread of the disease by rushing to hotspots of infectivity. They concluded, “Their behavior may have actually extended the course of the epidemic and altered its dynamics—for example, by keeping infected individuals alive long enough for them to continue spreading the disease, and by becoming infected themselves and being highly contagious when they rushed to another area.”

The researchers suggest that studying the behavior of the players can help predict the success of certain real-world measures, such as quarantines. “The failure of the quarantine measures… could not have been accurately predicted by numerical methods alone, since it was driven by human decisions and behavioral choices.”

Some of the behavior was to be expected. Many players reacted out of fear. Some blatantly ignored public health announcements. A lot of information — good and bad — was spread by word of mouth and trusted more readily than the official announcements from the game administrators.

Other behavior was a surprise. Some players were curious about Corrupted Blood, so they intentionally exposed themselves to locations of high disease outbreaks to see for themselves what the fuss was all about. “That’s something we [had] never put into the epidemiological model,” Fefferman says. In studying this behavior, they determined it was comparable to what happens when journalists intentionally travel to high-risk locations so they can report about events. By doing so, they raise awareness, but they also increase the likelihood of further spread of the disease.

While some of the experiences in the Corrupted Blood pandemic do not carry over well into real life (such as the infectivity rate of someone flying on a griffin from one area to another), much of the data has been useful. Fefferman says the data compiled during that time has proved invaluable in studying the spread and effectiveness of containment measures with COVID-19.

This may give you some solace if you find yourself unable to leave the house during this pandemic. You could always pass the time by playing video games. In so doing, you might be providing researchers with the very data needed to finally stop COVID-19 in its tracks.

Read more fun facts about video games.

Read more interesting facts about diseases.