Mathematical Model of Zombie Epidemics Reveals Two Types of Living-Dead Strains

KentuckyFC writes "Epidemiologists have long known how to model the way disease spreads through a population using a computer simulation. This generally involves three populations of individuals: those who are susceptible to disease, those who are infected and those who recover, return to the population and are no longer susceptible. Researchers then feed data about the number of infections and so on into the model which can then work out the disease characteristics such as infection rates. And with this information, they can predict the future evolution of the disease. Now researchers have used a similar model to simulate the spread of infection during a zombie epidemic. They've gathered infection data from real zombie movies, put this into the model and used it to predict the disease characteristics. The results show two clear types of zombie infection which differ in what happens to people after they die. In the first, epitomized by Night of the Living Dead, everybody who dies becomes a zombie. In the second, as in Shaun of the Dead, not everyone who dies becomes a zombie--contact with a zombie beforehand is required. This allows the interesting dynamic of escaping zombification by committing suicide. It also shows how close these zombies have come to winning. The research isn't entirely frivolous. The researchers say exactly the same process of model-building, data gathering and simulation works equally well on real diseases such as influenza. So their approach is a useful teaching tool for budding epidemiologists of the future."

Comments

Not exactly written by an expert

[ckatko]

>They then plug these figures into the model and iterate to find the set of parameters that best fit the data, a process known as Markov Chain Monte Carlo simulation. In total they run the simulations over up to 500,000 iterations.

The author makes Monte Carlo seem like a solver. It's not. You don't use Markov Chain Monte Carlo to model data. You use it to optimize finding solutions by reducing the number of samples required, which allows more complex models with less expensive hardware. You still need the rest of the picture to solve for the data.

That's like saying catalysts cause chemical reactions. No, they don't cause them, they help them go faster.

On the surface, this report seems absurd

[korbulon]

But this kind of pop media exposure is manna from heaven for researchers. The research itself is fatuous and risible, but the simple fact that a lot of eyes are now focused on these people means that the exposure of their "serious" work has been increased by several orders of magnitude. And often that's what really matters - not the underlying scientific value of your work - but that that work is attuned to tackle problems deemed more fashionable and relevant to society as a whole. Lacking a direct profit motive, fellowship committees have other priorities which are nevertheless rather worldly when determining the allocation of grant money.

End of the Epidemic

[RivenAleem]

If you assume an overnight conversion of 5% of America's population to Zombies (and not a gradual spread of infection) then you have 15.6 million survivors of 320 million people.

If only 1/3 of those people actively went hunting zombies, and managed to kill just one a day, All the zombies are dead in 2 months.

This is why I can't watch shows like The Walking Dead, where zombies are really easy to kill. The level of infection would never reach 95% in a real world scenario where you are required to be infected (by bite or scratch) and killed for it to spread.

According to Wikipedia, the US has an active manpower of almost 1.5 million people. When mobilised, It is safe to assume they with training and equipment they can kill at least 5 a day, meaning the epidemic is over in less than a fortnight.

Re:End of the Epidemic

[charon69]

"World War Z" (the book, not the movie) by Max Brooks actually covers this fairly well.

***Spoilers***

At least in my opinion, the zombies in WWZ are either some form of alien parasite, a nanite plague, or some equivalent mechanism that facilitates some rather severe changes in the zombies' biology. The internals have largely converted to a black, tar-like substance which appears to actually be providing the locomotive force. Gun shots, stab wounds, blunt beatings, etc. just pretty much don't do anything. They're spongy, soft, and simply absorb most impacts. There are no internal organs of any importance. The skeletal structure may or may not still be there, but any injury to it simply changes their mobility slightly. Their 100% immune to any bacterial, viral, or fungal infection, as whatever they've been transmuted into isn't compatible with local microbiology, so they don't rot or decay in any way, nor are do they appear susceptible to exposure. A zombie stuck in extended sub-freezing temperatures simply freezes solid and then thaws and returns to shambling around if and when temperatures increase. Trying to burn them is just as ineffective, as their new physiology has them slowly burn off their clothing and maybe an exterior layer of semi-normal-looking skin before the interior tar-substance makes the flames go out. To paraphrase the book, napalm is useless, as all you end up with is converting a bunch of slowly advancing zombies into a bunch of slowly advancing flaming zombies. And something else that the book goes into detail concerning is the complete and utter lack of fear. There is no such thing as using "shock and awe" tactics on something that literally doesn't care if it dies (since it's already dead anyway). The "Battle of Yonkers" shows this quite clearly, with the military using traditional tactics including large-scale artillery while the horde just continues advancing. A bomb might blow off a zombie's legs and throw it 20 feet to the side, but then the top half just starts clawing towards you again. Then you have the scale issues, as the numbers of infected eventually get so bad that those stuck up on the ISS can see them from space on the Midwest plains ebbing and flowing like herds of buffalo before Western colonization. And finally, you have the "call for help". The book describes the zombies calling to each other whenever "food" is located. And what's worse is that that sets off a chain reaction. Any zombie that hears a call-out will then call out again, so you have an ever-growing network effect where even just one zombie spotting you may be catastrophic. This lead to any roadway being a certain death trap. People would starve to death or dehydrate while trapped in their cars surrounded by zombies. The zombies never got to them, but then the person who died inside might become a zombie from latent infection. That car-trapped zombie then just became a standing warning signal. If somebody passed what appeared to be a deserted car on the road, and the trapped zombie noticed them, then it would call out, and any zombie in ear shot knew that dinner was served.

Tying this back to the original military-force problem, basically any military engagement would, therefore, draw enough attention that you were guaranteed a mass wave of them in a relatively short time frame. Combined with their nigh-invulnerability where literally *nothing* but a head shot was effective, and the military would simply run out of ammunition before they'd come close to dealing with the immediate threat.

Now I'm in no way saying that most zombie descriptions even come close to some of these details. And it's my understanding that Max Brooks' goal was to specifically modify the zombie milieu to account for any unbelievable aspect such as your assertion of military force being effective. So, yeah, in most cases you're right that artillery would probably work just fine. But if you're looking for somebody to try and actually make a *working* description of how a zombie plague might actually beat us, then try out the book. Avoid the movie, IMHO. It completely glosses over 90% of what I described above, which made it a standard, unbelievable scenario, unfortunately.

Re:Delayed Post

[Sarten-X]

The summary is crap.

The mathematical model that describes conventional epidemics is known as the susceptible- infected-recovered model. Individuals start off being uninfected but susceptible. When they come into contact with the disease, they become infected. And when they recover, they return to the general population but are no longer susceptible.

Back in 2009, researchers used this approach to build a simple model of zombie apocalypses. It suggests that zombies, once cured, return to the population to live out the rest of their years. And although no longer infectious, they are still zombies.

So a proper mathematical model of zombie epidemics has to allow for [zombie destruction]. Indeed, death is a potential outcome in many diseases so this kind of model better represents what goes in in the real world too.

In other words, most epidemic models assume a high chance of recovery and a low chance of reinfection. In some cases, fortunately rare in the real world, these assumptions don't hold true. The researchers therefore worked out a model that allows the infected to die permanently, then validated their methods using Markov Chain Monte Carlo simulations based off of information pulled from zombie movies.

The old model would accurately describe a flu outbreak, where a single strain of influenza runs through the population, but pretty much everyone survives and is then immune to reinfection. A worst-case epidemic, where a rapidly-mutating strain repeatedly infects the population with a high mortality rate, is better suited to this new model.