## Zombie plague analysed by Canadian maths prof

Quarantine, cure no good - violence is only hope

Posted in Science, 18th August 2009 11:43 GMT

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A Canadian infectious-diseases boffin has published an authoritative mathematical model of zombie plagues. He concludes that the only scenario in which our civilisation could survive a zombie outbreak is one in which normal humans react immediately using extreme violence against the undead, without any attempt to cure or quarantine them.

Professor Robert Smith? [1]* of Ottawa Uni is a mathematician specialising in the modelling of infectious diseases such as HIV/AIDS ("I started off in the rectal microbicide team, but then switched to the vaginal team. The jokes were never-ending, I can assure you"). Now he has turned his skills to analysing the fashion in which a zombie plague might affect the human population.

According to Smith?, a major factor restraining normal plagues from utterly devastating humanity is that they tend to kill their victims, after which the sufferers can no longer move about and infect others. This is one reason the frightful Ebola virus has never spread, for instance: it knocks people down and then kills them so fast that they have only a limited chance to pass it on.

Not so with zombification. Once someone has died of Z-plague, they remain a mobile carrier. The factors which have prevented humanity being rendered extinct by the Black Death, smallpox, cholera etc don't apply. Smith?'s models assume traditional dull-witted shuffler zombies rather than the nimbler types popular in some recent film offerings, but nonetheless the dynamics of undead contagion remain implacable.

In essence, as soon as there are any zombies in existence, humanity's only chance for survival is to instantly and effectively extirpate them. According to Smith?:

Human-zombie coexistence is impossible... Since all eigenvalues of the doomsday equilibrium are negative, it is asymptotically stable. It follows that, in a short outbreak, zombies will likely infect everyone.

He considers the use of schemes in which efforts are made to place zombies in quarantine of some sort, so rendering them unable to infect more people. Apparently this won't work: such a scheme can never completely contain the plague. It will therefore break out of confinement with disastrous results.

Likewise, even if a cure for zombification could be developed, it wouldn't work unless it also made the re-humanised undead immune to further infection. If it merely turned a zombie back into a human who could then be re-zombified once again, end results would be unpleasant. Some humans could survive, but only as a minority among the brain-scoffing swarms.

Suppose we are able to quickly produce a cure for ‘zombie-ism’. Our treatment would be able to allow the zombie individual to return to their human form again. Once human, however, the new human would again be susceptible to becoming a zombie; thus, our cure does not provide immunity... In this case, humans are not eradicated, but only exist in low numbers.

### Only instant, merciless violence can save humanity

According to Smith?, the only plan which gives human civilisation a chance to survive fairly unscathed is immediate, efficient use of violence to kill zombies wherever and whenever found.

An outbreak of zombies infecting humans is likely to be disastrous, unless extremely aggressive tactics are employed against the undead... In summary, a zombie outbreak is likely to lead to the collapse of civilisation, unless it is dealt with quickly... the most effective way to contain the rise of the undead is to hit hard and hit often... Only sufficiently frequent attacks, with increasing force, will result in eradication, assuming the available resources can be mustered in time.

In movie terms then, if your friends or loved ones become zombies, you mustn't hope for a cure or allow them to remain undead in some sort of quarantine or imprisonment. The only hope is to put them down for good without hesitation or mercy - destruction of the brain is normally seen as the way to change undead to actually dead.

We here on the Reg defence desk haven't got any quarrel with Smith?'s maths, obviously, or with the way he extrapolates from movies and books auch as World War Z, Resident Evil etc. We do quibble slightly at the movies and books themselves, however, which generally underestimate by a long way the sheer amount of violence that even relatively poorly-equipped armed forces are able to bring into play. Forget about cricket bats and shotguns: we're talking here about automatic weapons, bunker busters, artillery, close air support. Nukes, if necessary. You really aren't going to last long against the human race in a real fight if your only tactic is to shuffle straight up the middle moaning to yourself and try to bite people to death. And there's no need to worry about whether you've scored a brain hit - with most of these weapons you tend to hit your enemy all over.

Smith?'s work assumes a kill ratio of 0.25 in attempts to wipe out zombies, but this is wildly unrealistic. Fighting physically impressive, intelligent humans with primitive equipment and some military organisation, modern armies would normally expect to slaughter thousands of enemies with negligible losses, using nothing heavier than today's company-level kit - as witness the colonial wars of the 19th century.

Against easily distinguished dull-witted shamblers without organisation or weapons, and reserving the option of using serious heavy weaponry as required, the zombies would simply not stand a chance. A kill ratio of thousands to one would be more appropriate. The end of Shaun of the Dead, in which the military turn up and unhurriedly blow away the zombies besieging the pub ("Section 1. Zombies, to your front. Fire") is far more realistic than the various apocalyptic visions offered in other films, World War Z etc.

But Smith? offers one last chilling insight, even assuming that anti-zombie efforts are successful. "The disease-free equilibrium is always unstable," he writes.

The zombie maths paper can be read here (pdf) [2]. ®

*"Smith?" is his real legal name, adopted because "you have no idea what it's like to be entirely invisible on Google... at least it differentiates me from that guy from The Cure. It's been 20 years now and sadly his career shows no sign of drying up."