A secret group of environmentalist ultra-extremists has engineered a virus (or virus-like pathogen) with the purpose of making all of humanity extinct (yes, including themselves). They are aware that humanity will fight back against this plague as soon as they notice lots of people dying. There would undoubtedly be efforts to create vaccines, quarantines, and maybe even long term sealed underground shelters.

To avoid all of this, the virus was engineered to initially be mistaken for a mild cold, so it would have time to spread. A newly infected person would experience one or two days of mild sneezing and sniffles, after which the virus would go dormant. During this time, they would spread the virus to everyone they had contact with. After several years of this, the virus should be able to infect 100% of the world's population without anyone noticing.

Then, on a specific predetermined day and time throughout the world, the virus suddenly would switch to "deadly mode". Every person on Earth would become horrifically ill at the same time. There can be no emergency response, no medical care, no quarantines, because all of the people who would do such things are too busy dying. Within 24 hours, everyone is dead.

My question is, by what mechanism could this super-virus suddenly become deadly? How could a virus (or other pathogen designed to be mistaken for a virus) change its behavior at a predetermined time? It seems like the possibilities fall into two broad categories: internal mechanisms (each virus particle has something inside it that acts like a clock), or external mechanisms (the virus can detect something in the environment that happens on a given date).

Note that my question is not "would this succeed in making humanity extinct?" (I personally believe it would not. This is the basis of my story, actually.)

My question is also not "Are there more effective ways to achieve this?" (Undoubtedly there are. This plan was created by crazy extremists, and they chose to do it this way for their own reasons.)

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    $\begingroup$ I think it would come down to How long between release and 'deadly'? you say several years to get to 100%, though I think I've seen data from the CDC that shows a worst case 70%, due to mutations of human DNA, you'd likely need 3-5 strains that all trigger the same way, yet even then maybe 1% of the pop would still be immune.. Caltech virologist Alice Huang said ""For a virus to kill all humans on Earth, it would have to kill rapidly, like a week or less," Huang said. "If it took any longer, the immune system would have time to attack it" $\endgroup$ Jun 4, 2018 at 3:20
  • $\begingroup$ wired.com/2012/01/scientific-doomsday-scenarios $\endgroup$ Jun 4, 2018 at 3:20
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    $\begingroup$ @BaneStar007 The answer to "How long between release and 'deadly'?" is "However long it takes". If it takes a decade or two, that's fine, as long as nobody notices the true purpose during this time. And having 3-5 strains, or even 50 or 60, is fine too. And even then, I agree there may be enough survivors for the plan to fail. But remember, my question is NOT "would it work?" The question is "what is the mechanism used to trigger the deadly phase?" $\endgroup$ Jun 4, 2018 at 4:04
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    $\begingroup$ @BaneStar007 The only strong requirement is that the deadly phase happens at the same time for every infected individual throughout the world. Everything else is flexible. $\endgroup$ Jun 4, 2018 at 5:14
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    $\begingroup$ <related>Plague Inc. $\endgroup$ Jun 4, 2018 at 11:19

6 Answers 6


Real biological systems are precise, but not that precise. You won't be able to do this simply.

You could take a lesson from Stuxnet. Stuxnet is one of a family of new hyper-advanced computer viruses that's been released over the past few years. It was designed with cryptographic keys, some of which were believed to be files present on the target machines. Very surgical.

You could release the virus and have it infect everyone. Have it attack the brain, similar to the now famous O. unilateralis, the fungus which attacks ants and infects their brains, turning them into zombies. However, we're going to need to be more subtle than that. Instead of turning them into zombies, you should make them hyper-attuned to a particular visual signal. For dramatic effect, we'll make it a particular pattern of saccades done with the eye. We already have tremendously advanced brain structures to track the movement of people's eyes to figure out what they are thinking, so you just have to hijack it.

Then, once everyone is affected and hyper-attuned to your signal, you inject one person with a virus which causes that saccade. If you want the process to be more precise, inject one person on each continent. They'll walk around, triggering other individuals, unlocking the "encrypted" part of the virus. This part causes them to begin doing almost the same saccade. Air travel will get everyone doing this within a few hours.

Now you have a timer that will work. A virus isn't going to be precise enough with its timing, but the human brain is a marvel at keeping time. It's also really good at identifying patterns. If the saccade comes with a "generation count," the disease can do a half-decent job of predicting how long it has been since patient-zero has been infected.

12 hours later, with the combined mental powers of the entire human race working to keep time and infect everyone, the brain unleashes the final trigger, encoded in the saccade, and the virus turns lethal.

As an added bonus, it creates a really frighteningly bad-ass set of survivors, who cover their eyes (or gouge them out) to fight blind, to avoid this signal. Of course, if you wanted to hit these fighters (and the blind community themselves), you could make it spread by touch as well. The human brain is amazing at processing complex tactile information.

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    $\begingroup$ This is... impressive and wrong at the same time at so many levels... +1000 If I could $\endgroup$
    – Shirkam
    Jun 11, 2018 at 7:24
  • $\begingroup$ You could do almost exactly this but with some chemical or biological catalyst. E.g. it makes everyone allergic to something that's not normally present (maybe a GM Plant of some sort), which is then introduced into the food supply unnoticed. $\endgroup$
    – JeffUK
    Jun 11, 2018 at 19:43
  • $\begingroup$ @JeffUK Definitely, but I wanted the body's ability to process information to be part of the mix. I wanted the important trigger to be something transmitted via a non-biological path because biological systems have a nasty tendency to mutate. I'd hate for my disease to get discovered because one lone virus mutated and killed a guy. Better to have a "bootloader" that's relatively benign, and transmit the payload using more reliable means =) $\endgroup$
    – Cort Ammon
    Jun 11, 2018 at 20:08

If you want to kill everyone globally at the same time, you need an external signal. That's going to need to be some kind of broadcast -- sound or EM. So, reverse engineering, that means we need a virus that makes humans susceptible to one of those two things.

Let's tackle EM since it's far easier to coat the world in a particular EM frequency than to get the same sound produced everywhere (EM you can do from satellite). Copper is a fascinating substance, biologically speaking. We need some in our bodies (see Wikipedia "Copper in health"), and it shows up in our diet. But there is one place in the body where copper absolutely is not supposed to go -- into the brain. There are various things that can go wrong with the liver such that copper goes into the bloodstream and allows copper to go into the brain (it crosses the blood-brain boundary nicely). Copper is electrically conductive and can cause all sorts of problems when it shorts out circuits in the brain.

So... let's say you have a virus that encapsulates copper -- it keeps a few atoms of copper in its payload, sealed up and insulated so they don't mess with surrounding tissues. It replicates in the liver or digestive tract where it can harvest more copper. It spreads, targeting the brain. The virus finds a way to hide in the brain (some sort of trick to hide from the immune system). When the virus dies, it leaves the still-insulated copper behind.

You fire your EM pulse in the sky and it is strong enough to breech that insulation. Copper has resistance, generates heat, melts through the insulation, now it is in the brain. People start shorting out (literally).

There's some details to work out, obviously, but I think that rough sketch gets you where you're wanting to go.


To quote Cort Ammon, "real biological systems are precise, but that that precise. You won't be able to do this simply".

What timing signals are there that are available to the virus?

seasonal changes

There are several changes (e.g. hormonal) that take place with reasonable periodicity and that the virus can intercept. It can have two slow mechanisms, one that is triggered by the change, one that "rearms" the first mechanism; and these can be made to be transmissible, and have only a given number of iterations before triggering the final event.

external signal

This is difficult as we would need something that's almost ubiquitous, and at that point we've just moved the turtle elsewhere. Infecting the water supply of the whole planet with the virus trigger is no less difficult than doing so with the lethal virus.

syncing from other viruses

We want to avoid advance warning, so the timing mechanism is programmed to err on the side of caution. Instead of having 10% triggering early, 80% on time, and 10% late, we'll have 70% trigger on time, and 30% late. That 30% we can then try and recover by making the virus also trigger on detecting its own activated form.

This will also cause an abnormal "infection" mechanism in which the lethal version of the virus seems to infect a human within a few minutes and even in minuscule quantities, while it is actually activating the dormant version of the virus which is already there. Then, the "real" infection in someone that has been freshly infected will cause no symptoms for up to several days, but that person is still infective and contagious, and capable of triggering the virus in untriggered infected people.


It's pretty difficult to set up a sophisticated timing mechanism with a virus, because a virus can't really do anything internally; it has to reprogram other cells to do whatever it needs. Furthermore, a virus can only really reproduce by killing host cells, making it more difficult for the virus to appear harmless while spreading. Also, a virus lacks any mechanisms to regulate mutations (it would be kind of awkward if a mutant strain of the virus sent out the activation signal early, defeating the purpose of a delayed trigger).

For these reasons, I believe some kind of antibiotic-resistant bacteria may in fact be more plausible. There is already a strong precedent for certain strains of bacteria spreading to basically everyone while apparently harmless. In fact, by cell count, the human body has more symbiotic bacteria in it than human cells.

To set a trigger for this disease... You need something that you can be pretty sure won't accidentally trigger before the time you set, especially if the disease is programmed to propagate whatever activation signal you choose. You also need something that a disease can reliably pick up on and respond to at the correct time. Something chemical-based comes to mind, roughly equivalent to how a hormone is meant to function in more complex life forms.

So, say the bacteria mostly lives in the subject's lungs. Also, let's pick a trigger chemical that forms either a gas or aerosol at room temperature, and does not occur naturally.

Once an infected individual inhales a little bit of the trigger compound, the bacteria starts synthesizing more of the trigger chemical in the subject's lungs, which will be exhaled. The activation signal would spread very, very quickly, because as soon as a subject is exposed to even a tiny bit of the signal chemical, a bunch of pre-placed bacteria fires up to start cranking out more of the stuff.

The bacteria is coded to start killing the subject the moment it gets triggered (or, alternately, if the trigger chemical is toxic to humans the bacteria doesn't even need to do any additional work). The method of killing is fast, but generally takes a handful of hours to notice.

When the bad guys want to activate the disease, they can expose random densely populated places around the world to the trigger chemical, and then keep doing that until they are stopped. As a redundancy, they could also send out a bunch of packages across the world containing samples of the signal chemical, timed to arrive just a short duration after the initial release of the signal.

  • $\begingroup$ Do you have a source for "In fact, by cell count, the human body has more symbiotic bacteria in it than human cells." $\endgroup$
    – NomadMaker
    May 16, 2020 at 18:06
  • $\begingroup$ @NomadMaker I wasn't saying that with a particular source in mind, but I will refer you to a Wikipedia page on the subject (en.wikipedia.org/wiki/Human_microbiome#Relative_numbers). The exact ratio is often exaggerated, but it remains fairly likely that there are more bacterial cells than human cells within a given human body, and a pretty big fraction of those bacteria are symbiotic or at least not actively harmful. $\endgroup$ May 23, 2020 at 4:51

Maybe the team could "discover" the virus and tell the world about it once a lot of people have been infected and they could then create a fake cure/vaccine that, in reality, activates the virus after a while. The deaths from activated virus could spread this "activated virus" or could activate other dormant viruses through airborne particles or something.

The best, in my opinion, would be to tell the public about this new virus once it spread. Then, you activate the virus in some subjects (kidnap them or something to inject them the fake cure). Afterwards, tell the public that it is a potentially deadly virus and could manifest itself at any time to create panic and an urge for a cure (maybe activate even more subjects to rise the death toll and/or death rate). You could then explain that people die after the cure because the cure/vaccine was taken too late and that it is urgent that the public take the cure/vaccine as soon as possible.

If you want something with less involvement, you could make it react to pollen but the virus might go off prematurely.


You have two times to consider: the "subjective" time, counting when a single individual was infected, and the "absolute" time, counting the date when you want the switch to happen.

Internal mechanisms (i.e. telomere degradation) would work well for subjective time, but they would be impossible to synchronize. And you want all the death to happen at the very same moment, not 10 years (just to put a number) after the individual was infected.

External mechanism might be more tricky to implement, as it's hard to give a receiving system to a virus. But you can work in the following way:

Once the virus has gone silent into all the hosts, you can spread another virus, which specifically attacks the silent virus, causing a genetic modification that switches it from silent to deadly mode. At this point your only delay will be the diffusion among individuals. If the virus is found out and tested, during in vitro test it won't attack human cells (those samples cannot be infected by the first virus), so this will further delay the reaction.

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    $\begingroup$ This then makes the second virus the stoppable contagion, subverting the pre-spreading logic. $\endgroup$
    – bukwyrm
    Jun 4, 2018 at 5:13
  • $\begingroup$ @bukwyrm, the second virus won't attack human cells. $\endgroup$
    – L.Dutch
    Jun 4, 2018 at 5:18

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