EpidemicsControlling contagion by restricting mobility
In an epidemic or a bioterrorist attack, the response of government officials could range from a drastic restriction of mobility — imposed isolation or total lockdown of a city — to moderate travel restrictions in some areas or simple suggestions that people remain at home. Deciding to institute any measure would require officials to weigh the costs and benefits of action, but at present there is little data to guide them on the question of how disease spreads through transportation networks. A new MIT study shows that in the face of an epidemic, even moderate government-mandated travel restrictions would slow contagion.
In an epidemic or a bioterrorist attack, the response of government officials could range from a drastic restriction of mobility — imposed isolation or total lockdown of a city — to moderate travel restrictions in some areas or simple suggestions that people remain at home. Deciding to institute any measure would require officials to weigh the costs and benefits of action, but at present there is little data to guide them on the question of how disease spreads through transportation networks.
However, a new MIT study comparing contagion rates in two scenarios — with and without travel restrictions — shows that even moderate measures of mobility restriction would be effective in controlling contagion in densely populated areas with highly interconnected road and transit networks. The researchers called the difference between infection rates in the 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.
The study, published online 31 July in the Journal of the Royal Society Interface, is the first to link the concept of price of anarchy to the spread of contagion. It assumes that transmission of the news of the epidemic (which influences how people select travel routes) and the epidemic itself follow the same mobility network, and uses standard epidemiological models to simulate the flow of contagion.
The researchers — Ruben Juanes, the ARCO Associate Professor in Energy Studies in MIT’s Department of Civil and Environmental Engineering, graduate student Christos Nicolaides, and research associate Luis Cueto-Felgueroso — used data from the 2000 U.S. census to establish the aggregate daily flux of people commuting between counties.
Previous research had shown that when individuals become aware of an epidemic, they travel not by taking the shortest route, but by taking the shortest route that avoids infected areas — even if they’re already infected — a strategy that exposes people in uninfected areas to disease. Such “selfish behavior,” as it is called in game theory, is in direct opposition to the strategy of policymakers, who presumably would act in the benefit of the greater social good by routing infected individuals through areas where infection rates were already high.
The MIT study shows that the price of anarchy in some regions of the United States, such as along Interstate 95 in the Northeast, would be considerable. For a moderately contagious disease — one in which every infected person
