Earth-Year: 2618.
Location: Planet Hope, Proxima Centauri.
Terraformation status: 97.8% Earth-like.
Population: 128.596.

The residents of this planet live in a paradise-like environment. The gravity and atmosphere is almost identical to Earth. 25% of Earth's flora and fauna, the most important species, are successfully imported and maintain a stable population, covering the whole planet.

In any case, if one would happen to be teleported from Earth, for long he wouldn't notice any difference.

The people live an exceptionally long life. Accepted age of death is 130.

Colonizers were selected after a strict genetic filtering to minimize proneness of illnesses, cancer, defects etc. After colonization was finished, the colony imposed a very strict no-entry rule for non-Hope people. Then, to eliminate as many earth-originated illnesses as possible, the community entered a complete isolated lockdown lasting for exactly 1 Earth-year.

This quarantine included:

  1. Complete isolation of every resident from each other, in their own distinct, fully equipped apartment assigned by the Colonization Council. The doors were physically locked by authority, and any breach were severely punished. Breach of quarantine was neglectably rare.
  2. Family members were also isolated from each other. Children under 10 years at the beginning of the lockdown were allowed to stay with one of their parents.
  3. Physical delivery of any items was minimized to the highest possible degree. Any delivery happened by completely sterilized drones. All the delivered items - food or objects - were sterilized.
  4. All communication happened by VR Videocalling. Such a call makes the other party appear like in person, but physical contact, the feeling of touch, is not possible.
  5. All work where humans were needed was possible to be conducted from home-office. Physical presence was replaced by remote-controlled autonomous drones/robots.
  6. Every resident had to test himself each week. The test showed the presence of 99.9% of the most prominent bacterial, viral, fungal pathogens and genetic illnesses by an accuracy of 98%.
  7. Any positive tests were given their respective cure if it existed. In the very rare cases with no possible cure, the person was allowed a choice between relocation to another colony or Earth, remaining in quarantine for the rest of his life, or euthanasia.
  8. All infrastructure - water, waste, air - is completely sterilized. Sterilization happens at the very apartment before entering and after leaving, and also at any place where there is a remote chance of human interaction.
  9. People were allowed to keep at most one pet per person. Allowed pets were cats, dogs, or domestic rats. These animals were also included in the quarantine, and both the animal and their owner were tested for the respective animal's known pathogens in a similar way as human pathogens, excluding genetic tests.
  10. After one year, only those who hadn't shown the presence of any illness for 5 consecutive months were allowed to finish quarantine. Those who had, had to wait until they fulfilled this condition.


Is the above method sufficient to eliminate 99.9% of the illnesses occurring on Earth, and to reach a population with no/minimal illnesses - at least for a period?

What is my aim? The story is mostly inspired by COVID-19. I want to have a society which is totally vulnerable to all Earth illnesses. My protagonist would be a pilot in trouble from Earth, who breaches the isolation after an emergency landing, not knowing about the society; and causes a very bad outbreak - analogous to the Indians meeting with Europe - killing most of this society - making it necessary to enforce another quarantine. This time though the society is not well-prepared, and numerous troubles arise.

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    $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – L.Dutch
    Commented Jan 25, 2021 at 3:19
  • $\begingroup$ I'm sure there was an xkcd what-if on this, but I couldn't find it on the site. Maybe it was only in the book? $\endgroup$
    – sdfgeoff
    Commented Jan 25, 2021 at 21:28
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    $\begingroup$ No. Check out the history on Wikipedia of Typhoid Mary. She was completely infected with typhoid permanently although she herself suffered no ill effects. She was eventually contained on an island. $\endgroup$
    – SRM
    Commented Jan 25, 2021 at 23:52
  • $\begingroup$ @SRM She would've been caught by tests (point 6), and then either cured or taken care of (point 7), wouldn't she? $\endgroup$
    – Neinstein
    Commented Jan 26, 2021 at 18:59
  • $\begingroup$ @neinstein Depends. Many tests work by looking for antibodies. She didn’t have the antibodies... her body just lived with the disease instead of fighting it, as I understand the medical history. She wasn’t “asymptomatic”... she was “fully adapted”. Biology is clever enough and varied enough that I think it highly likely that something, possibly quite big, will slip through. 99% isn’t that good when it only takes one case to restart. $\endgroup$
    – SRM
    Commented Jan 26, 2021 at 21:56

10 Answers 10


Only for SOME types of illnesses. Even then there are problems.

Some illnesses are not infectious. That means quarantine does nothing to slow them down.

(a) Genetic illnesses. For example autoimmune diseases such as Crohns, MS and ATP.

(b) Cancer.

(c) Chronic side effects of past injuries.

(d) Mental illnesses and associated physical comorbidity.

(e) Self inflicted illnesses such as acquired diabetes, alcoholism, and all the bodily damage caused by them.

(f) Natural effects of being old. For example joint failure, and arthritis.

(Okay maybe quarantine will slow down (a) due to slowed reproduction rates. Or perhaps it will INCREASE reproduction rates due to boredom.)

From what I understand most medical care is not for curable conditions, but is routine maintenance for people with chronic conditions.

Even considering infectious illnesses (bacteria and viruses) there are reasons this won't work.

  1. Carriers: It is possible to be immune to a disease but still infect others. You carry the infectious cells in your body where they do no harm. But when you exhale into someone else's lungs for example they start doing harm.

  2. Animals: Animals can carry disease that can spread to humans, or evolve to do so.

  3. Weakened Immune System: By not exposing yourself to pathogens you weaken your immune system, and are more likely to get sick when you re-expose yourself.

  4. Incurable Diseases: For example HIV will not be cured by quarantine. There will be just as many people with the virus after as before. Well perhaps there will be less due to the restricted access to medical care caused by the quarantine. . . .

  5. Dormant Diseases: AlexP and Innovine point out some pathogens have a life cycle where they exist dormant in the body for years at the time. During that time you have no symptoms and are not contagious, and have no immunity, since your body is not fighting the disease yet. Thn years later you suddenly become sick and infectious. One year of quarantine will do nothing to those guys.

Now you will certainly slow down a lot of human-carried illnesses with this quarantine measure. But depending on how severe point 3 is (I don't know myself) it might be a BAD idea to do such a big quarantine, unless there was some particularly dangerous illness we were trying to get rid of.

Edit: For plot purposes I suggest you limit yourself to some particular type of illness being eradicated on the colony. This has been done at least once in human history with Smallpox. Another option is that something new evolved on Earth after the colony was established. Hence the colonists have no immunity to it.

Edit Edit: I am certain there is an episode of Star Trek where this happens. In some episodes the transporter beam has a scrubber that leaves behind any harmful cells or anything that is not supposed to be there. That means illnesses that develop on different planets never meet, and if someone suddenly arrives without transporter, they have no immune system for the local bacteria.

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – L.Dutch
    Commented Jan 25, 2021 at 17:35

That approach might work for eradicating most illnesses, however it poses a strong risk for developing autoimmune diseases and allergies.

As I explored in a previous question, there are suggestions that the lack of usage might drive the immune system out of its intended mandate.

Segregating people alone, with no contact with unclean objects, apart from the psychological burden, will put their immune systems on a forced vacation while they are supposed to be working 24/7. Some of them at least might develop autoimmune diseases or allergies.

That apart, there are illnesses with an incubation period longer than 1 year, for example Hansen's disease or some cases of rabies. For those your approach will fail. Same for illnesses caused by dormant viruses like Herpes Zoster.

I guess that people getting allergic to a simple hand-shake or a freshly squeezed orange juice might be an interesting twist for your story.

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    $\begingroup$ :s/most illnesses/some illnesses/ -- And those diseases for which it may work are typically benign. $\endgroup$
    – AlexP
    Commented Jan 22, 2021 at 12:51
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    $\begingroup$ Hermits have holed up for a year or more without collapsing immune systems, and things like the smallpox vaccine grant solid protection for 3-5 years, which indicates a fairly long memory for our immune cells even without ongoing exposures. $\endgroup$
    – ceejayoz
    Commented Jan 22, 2021 at 19:40
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    $\begingroup$ But hermits didn't live in a sterile environment receiving sterile food and water. The contrary I would say. $\endgroup$
    – L.Dutch
    Commented Jan 22, 2021 at 19:46
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    $\begingroup$ "That apart, there are illnesses with an incubation period longer than 1 year, for example Hansen's disease or some cases of rabies. For those your approach will fail." - isnt this adequately covered by points 6 and 7 of the question (tests / cures / exile)? $\endgroup$
    – JBentley
    Commented Jan 22, 2021 at 20:13
  • $\begingroup$ @JBentley OP indicates that testing only has 98% accuracy, so with a large population you'd expect some cases to slip through. $\endgroup$
    – G_B
    Commented Jan 24, 2021 at 2:48

Good idea, but there are some issues

You did say "99.9%", I'm not sure exactly whether my issues are 0.1% or not, but here are the ones I found:

Some people have poor immune systems:

First - I'm going to direct you to a chapter of the book "What if" in which Randle Monroe delves into this exact topic (was written pre-covid even). The author was nice enough to scan his own book in and post the relevant chapter on twitter after Covid19 got real.

To summarise Randle Monroe's work - a non-trivial percentage of the worlds population have crap immune systems and will never be perfectly cured. In your case, if those rules are rigorously enforced, they will die of old age in quarantine, commit suicide when they realise they can't escape, or the government just wipes them out Final Solution style after a few years of constant positive test results.

There are cases where this becomes a choice between two evils. I have a partner with MS, while on her medication her immune system is compromised, off her medication her nervous system decays. She'll have to pick between being in quarantine forever or being stuck in a wheelchair for life. At 18 she was a perfectly healthy human who would've been included in your society and passed all the screening tests, even with an unrelated MRI showing no lesions at age 19.

You'll need to find and remove all natural reservoirs for disease:

However not covered in that work, is the concept of a natural reservoir. These are humans or animals who are able to keep a disease alive "on or within them" without showing symptoms or even nescicarily testing positive. Diseases will hide there and resurface long after they've been eradicated.

Some diseases take longer than 1 year to show symptoms for:

You will also have issues with diseases that remain hidden for longer than 1 year. Herpes / coldsores can remain hidden for decades. I had a number of facial infections (ear, tooth, and bells palsy) spread over about 5 years that the doctor reckons was the same underlying infection slowly migrating.

My partners MS also counts here. We have no idea of the underlying cause, but it slowly appeared after exertion at age 23.

You will also have issues with people carrying such small amounts of disease they don't test positive or show symptoms

I can not find the link now, but I read somewhere that the reason we believe children to be at low risk of covid19 isn't because they are actually low risk, but because their immune system is more efficient in fighting them in the nasal cavity we swab while testing. Schools are full of covid19 but children keep falsely testing negative simply because they're noses are covid-free.

Another take on this is HIV. After sticking to your HIV meds for a while you'll be classed as Undetectable viral load. This means you can't pass on HIV to anyone else, and it can't be detected in blood by labratories, and your tests return negative. Stop taking the meds, and you may eventually become infectious again.

You don't need this quarantine for your plot

The American Indians didn't spent a year socially distancing in disinfected apartments after they migrated to the American continent. They just were separated from Europeans for a millennia or so. You can recreate that by keeping your population separate from Earth for a few generations, which may happen naturally for a space colony anyway.


Anthrax spores have been known to survive in the soil for as long as 48 years

But perhaps you're asking only about viruses. These survive better in water, I think.

In cool groundwater at 4 degrees C, 10% of MS2 bacteriophage viruses can survive for 83 days, and if we can assume that survivability is linear, a year would reduce the levels to 1/1000th. (I'm assuming "1-log" means "one tenth": it's not a term I've heard before, could mean 1/e maybe?)

Hepatitis A virus, which is known to be transmitted through fecally infected drinking water, was found to be still infectious in mineral water after 300 days at room temperature, and to survive far longer at lower temperatures: at 4 degrees C, it took 519 days to reduce viral activation even to 1/10th (well, to "1-log" whatever the hell a 1-log is).

Viruses can be frozen essentially indefinitely. A virus was recovered from permafrost after 30 thousand years, raising concerns that global warming could unlock ancient plagues from the frozen ground.

Importing the most important macroscopic flora and fauna from Earth, would mean there'd definitely also be vectors for novel diseases that could then jump to humans.

We can't get rid of all microscopic life. Microbiomes are important. While estimates vary, the human microbiome is so significant that it comprises somewhere between 50% and 90% of the cells in our bodies.

But all that said: plagues, and novel viral mutations, are a game of Russian roulette. If you reduce the population of the world to 1/60,000th of the Earth's population, then even without quarantining, the chances of a plague are 1/60,000th of the chances on Earth. The odds of a mutation happening in someone's intestinal e coli to make it deadly are lower because there are far fewer someones that it could happen to.

Consider that I live in a small city of some 128,000 people. Naively, the odds of a pandemic starting on that planet are the same as the odds of a pandemic starting in my city.

Then reduce that by the amount of extra separation they get being on a whole planet instead of just a city - how often do they attend potential "super-spreader" events with more than a dozen people in? Probably not often.

And reduce it again by the amount of variation they removed from the world's microbiome when migrating the macroscopic flora and fauna. Did they remove the earth from plant roots? Irradiate them and bathe them in UV? Dose the animals with antibiotics and antibacterial enemas, quarantine them, and so forth? They'll all initially be sickly because their microbiomes will be deficient, but the survivors will have less disease.

BUT! Then multiply that by the weakness of the peoples' immune systems. Do they play in the dirt as kids? Do they catch diseases at a low level and have their immune systems destroy them without ever noticing? If not, then they will be left uniquely vulnerable to even a fairly mild plague.



While it's possible that you might get rid of (let's face it: comparatively minor) diseases like the common cold, there are many diseases which this won't do anything about.

For the sake of time, I'll only mention the two most common types: STDs and Zoonotics.

  • STDs: These generally last for your whole life, unless you happen to treat them early enough. Plus, the most nasty ones have an incubation period of decades. While you can test for these (with, as Luann pointed out, mixed results), the only practical way to get rid of STDs is to kill everybody that's infected, and most people wouldn't consider that an option.
  • Zoonotics: While it's theoretically possible to keep all the humans in quarantine for a year, doing it for every animal on earth isn't. Even if you could somehow manage to quarantine every single animal on the planet, it wouldn't get rid of many zoonotics; they're often harmless in their home species. Also, some diseases (such as tetanus) are caused by bacteria which are endemic in soil and on most surfaces. These are normally kept out by the skin, but can cause issues if they nevertheless manage to enter the body. Quarantine wouldn't do a thing against this subcategory; they don't need animals to survive.

Even if you do get rid of all diseases, you're seriously screwing over later generations. By getting rid of all diseases, you're also getting rid of the need for an immune system. This means two things:

  1. Any diseases which pop up later will be extremely deadly, and there'll be hardly anything the colonists can do to stop them.
  2. They'll never be able to visit earth (or any un-sterilized colonies), as the common cold would be a death sentence.
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    $\begingroup$ There's STDs with an incubation period of decades? What? That's more evil than The Daleks! $\endgroup$
    – J. Mini
    Commented Jan 24, 2021 at 0:41
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    $\begingroup$ @J.Mini You don't have to go far. Aids has an incubation period of on average 12 years. That's why I want to test everyone weekly instead of just waiting for symptoms. Technically long ilnesses with no cure will be taken care by the (arguably inhuman) 7th point of mine. Zoonotics are a fair problem, but works for my plot as they are novel diseases not present on Earth. $\endgroup$
    – Neinstein
    Commented Jan 24, 2021 at 11:44
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    $\begingroup$ @Neinstein HIV is more devious than that. The virus can hang out in healthy cells without doing anything, neither testing nor the immune system know anything about it, the person becomes completely healthy thanks to anti-viral treatments... and then suddenly (probably at random) the virus starts working again. There's other viruses that can use healthy cells as their reservoirs, and there's plenty of normally harmless "alien life" in and on humans that can cause disease under certain conditions. $\endgroup$
    – Luaan
    Commented Jan 25, 2021 at 10:33
  • $\begingroup$ Me, im a std anti-masker, i think i have a right to spread the itch, or itch the scratch.. $\endgroup$
    – Pica
    Commented Feb 14 at 14:38
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    $\begingroup$ then you have good old retroviruses which edit themselves in to your DNA, so once you have them once you have them forever. $\endgroup$
    – John
    Commented Feb 16 at 0:24

Never say never Even with that strategy you can reduce many illness to old memories but there is many point to consider. First of all is that many things are just caused by human activity and does not depend on contamination (pneumonia, get a cold as exemple). So even in the best scenario it is not possible to avoid the body reaction to an environnement.

Another point to consider is that virus and other vector can evolve and even new one can rise. If you let nature do one year you can't imagine what could rise on the next 10 years. Speaking of Covid it is a brand new virus and this is the problem, no cure, no vaccine and no immune system memory to fight it in the correct way so this could happen the week after the year of lockdown that is not impossible.

Finally if you want a population that doesn't have any illness and you succeed perfectly to avoid the previous point i pointed there is the big one : you need a population. Even with the best intention you have many mental issues that this lockdown will create and one year can be enough for many suicide. With all of this lockdown many people will develop issue to interact with other people and you may reach a point where not so much people will return to a normal life and a whole generation will be sacrified. Other main point is that one year of lockdown will be one year without newborn, and with the suicide and people excluded because they were ill it will lead to a very very big crash on the demography. And not only for the next year but for many years, even generations. People doesn't take the same time to decide if they will make a baby, so for many years the generation will be very low.

For me this theory is interesting to discuss because it is utilitarian vision but human being is not meant for being alone in a house, as proof history is based on creating civilization and not every individual building something.

Hope my bad english doesn't affect too much the point i tried to develop.

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    $\begingroup$ Don’t forget illnesses caused by otherwise benign bacteria. Meningococcus is perfectly OK living on skin, but much less so if it’s in your spine. $\endgroup$
    – Joe Bloggs
    Commented Jan 22, 2021 at 10:40

Many diseases are caused by bacteria. They can live (or survive while dormant) in many environments, from space to kilometres deep in solid rock to being frozen in the Arctic tundra for millennia.

Bacteria are also fundamental to our biology and the Earth ecosystem. There can be no life without them. So your idea of a perfectly sterile planet is a dead planet.

There is no way you can remove them all, nor that you could somehow remove the ones considered "harmful". Many of them are indispensable in one context (decomposing poo into plant food) but deadly in another (try eating it).

  • $\begingroup$ Yep, there's all kinds of bacteria around. Some are good while some are bad. Anything fermented: cheese, sour cream, kombucha, kimchi, sauerkraut, beer, bread, chip dip, and so much more all has bacteria in it, some of them active. "Probiotics" are the results of bacteria. And you can't kill the bad bacteria without killing the good bacteria. And how do you kill it? Heat or radiation? Heating it will cook it, changing it's chemical composition. Radiation means having radiation sources everywhere to do the sterilization without creating bottlenecks for distribution. $\endgroup$ Commented Jan 25, 2021 at 17:14

During 1 year, the bacteria & viruses causing diseases could mutate into new strains. The folks quarantined with the new strain might build up an immunity, but other folks quarantined other places wouldn't have experienced it yet. So, when folks start interacting after a year, there could be many slightly different strains of disease all interacting at once. It could put a burden on the human immune system trying to fight off a lot of new variants at one time.

EG: after a year, one quarantine place had some colds, and a new cold virus mutated. Another place got the flu, and a new flu virus showed up there. Etc, etc. Once quarantine was up, folks interact. Folks that have never experienced the latest cold & flu could get hit with them at the same time.. one hits them, weakens their immune system, so the next is right in line. This could create a cascade effect of illness.. which might overwhelm some folks (eg: elderly).

Think of it this way... when kids are born, they are sick almost non-stop. Their bodies spend the first few years building up immunity to all the stuff out there, and they're constantly bombarded by it. They're non-stop buckets of illness -- snotting, puking, etc everywhere as they get sick and their body builds up an antibody library. They get over it, because they're young and relatively healthy.

Now quarantine everyone for a year. Virus strains mutate just enough to create a new yearly flu that folks can get even if they've previously had the flu. So, it stands to reckon they will still mutate in someone's quarantine.

Now remove quarantine after a year. All the mutated virus, etc hit every at once. Elderly, immuno-compromised, etc folks could get wiped out.

Quarantines work to isolate very deadly diseases / infections. But, humans were designed to interact and share illness in order to keep up with the latest mutations in disease. When something really nasty shows up (EG: people dying right and left), quarantining can help as a last resort to try to isolate and snuff it out. But, long term quarantine and isolation won't make everything go away, it'll just lead to weaker humans with weaker immune responses getting hit by many variants at once when they start going out and interacting again.


Skip the Quarantine, go with incubator-grown populations:

If you want a starting population utterly scrubbed free of communicable diseases, the old-school standard for sci-fi is to have a population grown entirely from embryos, and raised in the first generation by computers and robots. In a colonization scenario, it makes a lot of sense. The initial wave of human interstellar colonization could be carried out by slower-than-light ships that still go very fast.

But transporting whole living humans is VERY problematic for centuries. The solution? genetically selected or engineered embryos are grown into babies inside incubators on arrival to the planet. If need be, they are genetically modified to adapt to local conditions based on preset parameters.

Every embryo is selected on Earth to be free of any disease that can be eliminated. With good enough biology, the embryos may be completely manufactured and never have come in contact with any communicable disease. Even predilections for mental illness can be selected out. The same conditions are applied to all imported Earth life.

The only diseases would be things like soil or intestinal/skin bacteria that are also capable of causing opportunistic infections. You can't get rid of everything (sorry).

Naturally, your pilot sounds like he's got FTL technology. Subsequent FTL travel can bring the colonists up to speed on tech, but if they maintain separation from Earthlings they have no exposure to disease. Or maybe it's the FIRST contact they have with FTL-capable humans. Or subsequent slower-than-light travel is much better/cryogenics is improved/etc. That's up to you.

  • $\begingroup$ Disease-free humans would have horrible immune systems, and would die pretty soon. $\endgroup$
    – RonJohn
    Commented Jan 25, 2021 at 1:57
  • $\begingroup$ @RonJohn Not necessarily. The human immune system needs challenges because it has to respond to threats. If there are no threats, the immune system is still doing it's job. There IS an alien environment to confront, with plenty of immunogenic challenges. There will still be soil, skin, and intestinal bacteria present for the immune system to deal with. There's nothing magical about getting sick if there is no disease to be ready to fight off. But what it WILL do is make the locals exquisitely vulnerable to all the old-school Earth diseases - all the things the pilot will bring to them. $\endgroup$
    – DWKraus
    Commented Jan 25, 2021 at 2:25
  • $\begingroup$ @RonJohn If you have enough harmless Earth bacteria, they may even have a BETTER immune system, since thy would likely be extremely casual about cleanliness, what they touch and put into their mouths, etc. Since they have no diseases that are likely to make them ill from doing so. I'd be more concerned about people living in space stations/ships having poor immune systems due to lack of exposure to good old dirt. $\endgroup$
    – DWKraus
    Commented Jan 25, 2021 at 2:34
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    $\begingroup$ @RonJohn I don't mean to be grumpy about it. I have a Master's degree in cell biology and get a little passionate. I may not be explaining my self as well as I could. Does my last comment make more sense? $\endgroup$
    – DWKraus
    Commented Jan 25, 2021 at 3:30
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    $\begingroup$ @RonJohn Re read the aim section at the end of the question. Their stated aim was to have the planet struck by terrible diseases due to the arrival of an off-world pilot. The quarantine was the mechanism to achieve that immunogenic vulnerability, and I was just coming up with an alternative that would do a better job of eliminating disease than a quarantine. Plus, if you thought you could get away with your world never having infectious diseases (unrealistic, but...) you might think to make things that way, too. $\endgroup$
    – DWKraus
    Commented Jan 25, 2021 at 4:22

FRAME CHALLENGE: Why is it necessary for your established colony to undergo Quarantine, when it would be far easier and obvious to quarantine the settlers DURING TRANSIT to the colony planet? Not to mention, select only completely healthy people and purge their bodies with antibiotics and antivirals (+ surface sterilization) prior the boarding the colony ships.

This would feel much more natural, less cruel, and significantly less burdensome.


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