New study shows restriction of mobility could slow epidemic

Responding to an epidemic or bioterrorist attack with moderate travel restrictions could effectively control contagion in densely populated areas, according to a study published on Wednesday in the Journal of the Royal Society Interface.

The Massachusetts Institute of Technology study compared contagion rates in two scenarios, one with travel restrictions and one without the restrictions. Previous research showed that individuals who become aware of an epidemic travel by taking the shortest route to avoid infected areas, even if they are already infected. The behavior, known as selfish behavior in game theory, exposes people in uninfected areas to disease.

The researchers found that restricting individuals to specific travel routes would lower infection rates by as much as 50 percent. The research team called the difference between infection rates in the two scenarios the "price of anarchy."

"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," Ruben Juanes, one of the researchers on the study, said. "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."

The researchers tracked an infectious disease as it spread through commuting networks in the contiguous U.S. The price of anarchy varied depending on how close a network was to major commuting routes. The MIT study showed that the price of anarchy was high in some areas of the U.S., particularly along Interstate 95 in the northeast.

"Although the study is an idealized scenario, it does give insight to authorities about when and where it would be important to impose route restrictions on human mobility in the case of an emergent outbreak or in the extreme case of bioterrorism," Christos Nicolaides, the paper's first author, said. "But you have to take into account the structure of the underlying mobility network and its traffic properties. Imposing policy-initiated action in areas with low traffic would not render substantial benefits for the containment of an epidemic."

Dirk Brockmann, an associate professor of engineering sciences and applied mathematics at Northwestern University who was not involved with the study, said the paper could result in a major change to epidemic modeling.

"In my view the MIT paper could be a game-changer in the field of epidemic modeling," Brockmann said. "Including decision-making and game-theoretic components into models of disease dynamics is massively overdue and essential, as even the most sophisticated models do not account for this type of feedback. Since mobility is such a sensitive component in terms of shaping disease dynamics, the approach the researchers take is very plausible, and it identifies clearly the intriguing interplay of selfish action versus policy action in the context of epidemiology. This is going to be very important in the future."

Juanes said the next step with the study would be to measure the price of anarchy for epidemic contagion in the world's 7,000 airports.