The zombie apocalypse won’t take long.
A new article in a peer-reviewed student journal finds that the zombie hordes would take Earth’s population down to a mere 273 survivors in 100 days.
The paper, published in the University of Leicester’s Journal of Physics Special Topics, was a fanciful use of the so-called SIR model, which is used in epidemiology to simulate how diseases spread over time. It’s not the first time zombies have been used as a public health metaphor. In December 2015, for example, the British medical journal The Lancetpublished a tongue-in-cheek paper titled “Zombie infections: epidemiology, treatment, and prevention.” And the website of the Centers for Diseases Control and Prevention (CDC) once went viral with a blog post urging zombie apocalypse preparations as a metaphor for real-life disaster preparedness.
In the new analysis, the University of Leicester undergraduates assumed that each zombie would have 90 percent success at finding and infecting one human a day, a rate that would make the zombie virus twice as contagious as the Black Death, the plague that devastated Europe in the 1300s. [Zombie Animals: 5 Real Cases of Body-Snatching]
The researchers further estimated that each zombie could live 20 days without braaaaaains.
Assuming a starting population of 7.5 billion people, approximately the world’s population today, the students calculated that it would take 20 days for a single zombie to start an epidemic of noticeable proportions. At that point, the pandemic has begun. Assuming no geographic isolation, in fact, the human population would drop to 181 by day 100, with 190 million zombies roaming around.
With some geographical isolation, the situation would be a tiny bit better for humans. Assuming the zombie virus had to spread through contiguous regions and that zombies were somewhat limited in their ability to travel (not leaving their current region until there were 100,000 zombies roaming there), human survivors would number 273 by day 100.