Price of Anarchy: Controlling Contagion by Restricting Travel During an Epidemic

During an epidemic, contagious diseases can spread between cities and countries faster than ever. Infected patients travel on planes, in cars and on ships, bringing the contagion with them as they hop across borders and oceans.  Now, scientists have taken a look at these modes of transportation, revealing that contagion rates could be controlled in densely populated areas as long as travel was restricted.

The researchers examined two different scenarios if an epidemic were to occur. They called the difference between infection rates in these two scenarios the "price of anarchy," a concept from game theory that's frequently used as a metric in studies of the controlled use of transportation networks.  Essentially, it measures how the efficiency of a system degrades due to selfish behavior of its agents.

The researchers assumed that the transmission of the news of the epidemic and the epidemic itself would follow the same mobility network. They used standard epidemiological models to simulate the flow of contagion.

After examining the models, the researchers made some surprising findings. It turns out that the price of anarchy in some regions of the United States, such as along Interstate 95 in the Northeast, would be considerable. In fact, for a moderately contagious disease, restricting individuals to specific travel routes would decrease infection rates by as much as 50 percent.

"In an area with high connectivity, the outcome of action coordinated by officials is going to be better than selfish action, but the economic and social costs of disruption could sometimes be too high," said Ruben Juanes, one of the researchers, in a news release. "In other cases, there would be an enormous benefit to having authorities impose travel restrictions. The price of anarchy is a quantitative measure that identifies areas where intervention might pay off."

In the end, the researchers found that the price of anarchy for contagion varies depending on the proximity of a network to major commuting corridors. The next step for the researchers is to measure the price of anarchy for contagion in the world's 7,000 airports.

The findings are important for understanding exactly how an epidemic might affect the U.S. In addition, it shows how officials might be able to slow the spread of a contagion. Mobility is a sensitive component when it comes to disease dynamics, so learning as much as possible about how people will move during this situation is crucial for future scenarios.

The findings are published in the Journal of the Royal Society Interface.