Epidemiologists today worry a lot about swine flu. But earlier this year, Philip Munz got interested in a more devastating possibility: an outbreak of zombies. A graduate student at Carleton University in Ottawa, he was watching a lot of movies about the undead and realized that zombification could be regarded as a classic paradigm of infectious spread: people get bitten by zombies, after which they turn into zombies themselves and start biting others. So Munz decided to use the tools of epidemiology to answer a sobering public-health question: could humanity survive a zombie outbreak?
Working with a professor and two other graduate students, Munz built a mathematical model of a city of one million residents, in which an outbreak occurs when a single zombie arrives in town. He based the speed of zombie infection on the general rules you see in George Romero movies: after getting bitten, people turn into zombies in 24 hours and sometimes don't realize what's happening to them until they change.
When he ran the model on a computer, the results were bleak. "After 7 to 10 days, everyone was dead or undead," he says. He tried several counterattacks. Quarantining the zombies didn't work; it only bought a few extra days of survival for humanity. Even creating a "cure" for zombification led to a grim result. It was possible to save 10 to 15 percent of the population, but everyone else was a zombie. (The cure in his model wasn't permanent; the cured could be rebitten and rezombified.)
There was only one winning solution: fighting back quickly and fiercely. If, after the first zombies emerge, humanity begins a policy of "eradication," then the zombies can be beaten. This is, as Munz points out, what traditionally saves humanity in zombie flicks. "People finally realize what's happened," he says, "and they call the army in." Or as he concludes in his paper on the work, to be published in the collection "Infectious Disease Modelling Research Progress": "The most effective way to contain the rise of the undead is to hit hard and hit often." CLIVE THOMPSON