John Smith is a time traveller from the year 2018, he goes back in time to the year 1200 and in the process falls in love with a woman of that era. He doesn't want to abandon her so he decides to bring her with him.

How would John protect her from modern disease - what realistic measures would he take to safeguard her? Would her immune system ever adapt to modern bacteria or is she doomed to suffer a dark fate?

The level of technology is the same except for time travel. Medicine is pretty much the same as today's.

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – a CVn Jan 31 '18 at 10:38

11 Answers 11


She would likely need a full round of vaccinations, just like everyone else in the modern world. If anything modern sanitary conditions would be less likely to spread diseases to her.

I would personally be more concerned about her starting new outbreaks of diseases here that had been effectively eradicated and are no longer generally vaccinated against. Are you up to date on your polio and smallpox inoculations?

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    $\begingroup$ If polio and smallpox didn't kill him when he was actually in the past (with no modern doctors) I bet it wouldn't be a problem when he comes back either. As for her being a carrier, he could just ask the doctor to test her when she shows up for vaccines. $\endgroup$ – Superbest Jan 27 '18 at 0:12
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    $\begingroup$ Would he not have taken a smallpox and polio vaccine? $\endgroup$ – Harper Jan 27 '18 at 0:27
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    $\begingroup$ I'm not even sure you could easily get a smallpox test anymore, and in the meanwhile, the high reproduction number of it means it is very likely to spread. $\endgroup$ – Nick T Jan 27 '18 at 6:36
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    $\begingroup$ @NickT Anyone doing time travel would easily have access to smallpox tests and vaccines. Even if he strongly insisted in not having such access... $\endgroup$ – Ville Niemi Jan 27 '18 at 14:23
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    $\begingroup$ @AngeloFuchs, In the US, the CDC has a large stockpile of smallpox vaccine just in case. In any case, quarantine protocols would have to be created to reduce the risk of cross-contamination between timelines (notice I used the word reduce, not prevent). Also, time travel could be a good way to collect fresh samples of old strains of diseases, so that new vaccines could be developed and stockpiled. And animals from the past could also be brought to the present to see how well their immune system would respond to new strains. $\endgroup$ – Stephan Branczyk Jan 28 '18 at 23:40

I think the things she's used to doing to safeguard herself in the 1200s from disease would be one of the things that would endanger her.

She'd want to do things like pee outdoors. She would probably not be used to clean water so, in our era, she would be drunk out of her mind most of the time. People back then drank a lot of beer because the water wasn't clean, but the alcohol content was very low.

Water from the tap would probably seem as repugnant to her as drinking out of a toilet for us. Sure we could do it if someone assured us it was clean. But viscerally you'd want to drink something else.

A reasonably intelligent informed person can avoid pathosis. There's the old cliche' about not drinking tap water in Mexico. And your body can get adapt over time.

But overcoming the danger to her from disease would be more psychological than physical.

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    $\begingroup$ She'll probably be overrun by a car, the first time she goes outside to pee while being intoxicated. $\endgroup$ – Abigail Jan 27 '18 at 19:00
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    $\begingroup$ This is a fantastic answer (+1), the others are pragmatic and interesting but this one was real fun. The other comment summarizing it as well. $\endgroup$ – WoJ Jan 27 '18 at 19:08
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    $\begingroup$ TIL the noise outside my flat on Saturday was actually time travellers from the 1200s. $\endgroup$ – Bilkokuya Jan 29 '18 at 9:58
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    $\begingroup$ Not true $\endgroup$ – Philippe Jan 29 '18 at 14:54
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    $\begingroup$ downvoted as the info about medieval people avoiding water is false: io9.gizmodo.com/… $\endgroup$ – Geoffrey Brent Jan 29 '18 at 20:27

Modern medicine is a marvelous thing. It is one of the primary reasons that life expectancy has more than doubled since the 1200s. The other major one being access to adequate nutrition. That alone will add years to their life expectancy.

We've become incredibly good at treating infections to the point where we have almost wiped a disease or two off the face of the earth. The 1200s were a time where there was a real risk of death from infection from even minor cuts. Today when someone dies from an infection from minor injury it makes the national news.

Anyone from the 1200s brought to the present will almost definitively live longer than they would were they left in their own time.

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    $\begingroup$ where we have almost wiped a disease or two off the face of the earth. Two actually, Smallpox and Rinderpest. Four more are still underway: Polio, Dracunculiasis, Yaws, and Malaria. Polio is effectively extinct globally, except for the underdeveloped Middle East and African countries. Malaria we're going to eradicate by eradicating mosquitos; Malaria is more of a side effect (intentionally, but its an attack on the infection vector rather than the disease itself, unlike with Polio and Smallpox which was immunized against). Smallpox still exists, too, but only for scienctific research $\endgroup$ – Draco18s Jan 26 '18 at 22:12
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    $\begingroup$ @Draco18s What humans can do when they decide to band together to uplift everyone is one of the most hopeful things I can think of. It gives me hope. $\endgroup$ – sphennings Jan 26 '18 at 22:15
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    $\begingroup$ @Draco18s This isn't right. Neither smallpox nor cowpox has a cure. They either go away on their own or kill you. The key is that contracting either makes you immune to both. Since cowpox almost never kills you, preemptive infection with cowpox means you'll never get smallpox, which often does kill you. If this sounds like a vaccine, that's because it is. In fact, it was the first vaccine--the word "vaccine" itself comes from the Latin for "cow". $\endgroup$ – eyeballfrog Jan 26 '18 at 23:03
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    $\begingroup$ @jamesqf the health problems caused by the 21st century western diet will kill you much later than living in the 1200s will. $\endgroup$ – sphennings Jan 27 '18 at 0:23
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    $\begingroup$ A correction for the opening paragraph: life expectancy FROM BIRTH was half of what it is now due to a far greater likelihood of dying during childbirth or childhood. If you survived into adulthood, your expected lifespan was into the 50s or 60s. At least for men (see childbirth). $\endgroup$ – jaxad0127 Jan 27 '18 at 2:12

I believe that, for diseases which the woman has never been exposed to, her immune system would be comparable to that of a newborn or young child - but she has the advantage of being an adult with a tougher body to withstand those. Your basic set of vaccinations should do the trick against most microbes. For any diseases for which a vaccine is not available, there is no knowing how she will fare until she does get those. I would suggest going to the doctor a little more often than most people do, at least in her first few years in the present.

Due notice that genetic drift is a thing even for humans, and that we may be immune to some things today because we are descendants of those who had the right genes. She may be less resistant to some diseases for which we are usually not vaccinated today, such as the black death - which peaked midway through the 1300's and is returning nowadays (4 deaths in the US in 2015).

One would think that the woman should need a liver transplant to withstand the caloric amount of foods nowadays, should she wish to eat like most people do. I'd just like to remind everyone that sugar became abundant in England around the Tudor period (stating at late 1400's).

  • $\begingroup$ Interesting... she would also face liver issues? Is the liver transplant thing an exaggeration or would she adapt? $\endgroup$ – Morgan Jan 26 '18 at 21:47
  • $\begingroup$ You're misreading that graph. There were 4 cases 0 death from the black plague in 2016 which is less than the yearly average of 7 cases. The odds of any one person being exposed to the black plague in their lifetime in the 21st century is extremely low. $\endgroup$ – sphennings Jan 26 '18 at 21:48
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    $\begingroup$ @Morgan she would in the very least get a fatty liver for sure. Untreated, it evolves to cirrhosis. $\endgroup$ – Renan Jan 26 '18 at 21:55
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    $\begingroup$ @Renan - "Eradication: Permanent reduction to zero of the worldwide incidence of infection caused by a specific agent as a result of deliberate efforts; intervention measures are no longer needed. Example: smallpox. Extinction: The specific infectious agent no longer exists in nature or in the laboratory. Example: none." – CDC. But I'm guessing they're ignoring Sweating sickness. $\endgroup$ – Mazura Jan 27 '18 at 0:06
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    $\begingroup$ Actually her immune system would be even less than that of a newborn. Different cultures have a certain level of genetic immunity in a type of molecule called MHC which, similar to antibodies, can bind to threats. Unlike antibodies, MHCs are entirely hereditary. Those with MHCs that are relevant to their environment survive. That's why Native Americans got fucked over so bad. A girl coming from 1200 would have MHC alleles great for the common pathogens back then, but most likely would be terribly ineffective today (and vise versa). $\endgroup$ – forest Jan 29 '18 at 2:56

Depends where she was. If she was European then she has a lot of immunities and would be pretty safe. But if she was a Pacific Islander for instance she could easily die of the most common diseases such as measles which almost depopulated many Islands. Or the common flu for that matter.

Many natives taken on exploration voyages were dead within a couple of years. Whole communities succumbed to flu and measles in days.

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    $\begingroup$ Exactly. We'd be at risk from her being a carrier of smallpox, german measles, etc which we have little immunity to anymore. $\endgroup$ – RonJohn Jan 27 '18 at 23:27
  • $\begingroup$ @RonJohn possibly but the general publics risk from contact with her is outside the scope of the question posed. $\endgroup$ – Kilisi Jan 28 '18 at 4:44

"One would think that the woman should need a liver transplant to withstand the caloric amount of foods nowadays, should she wish to eat like most people do. I'd just like to remind everyone that sugar became abundant in England around the Tudor period (stating at late 1400's)."

What a ridiculous exaggeration!

Firstly her hunger would be satiated a lot quicker, she'd just eat less. Do you think she'd stuff herself silly with fast food and ice cream just to be cool and fit in? She'd eat less: problem basically solved.

Secondly her body would adjust over time anyways. There are people who move, for example from remote jungle areas in the Amazon to big cities in Brazil and Peru. Guess what, they don't suddenly die from cirrhosis. Diabetes rates might be high among re-located indigenous people, but they also get diagnosed and treated over the course of many years. "Renan" is reading too much "diet" books that hype the harmfulness of sugar (and usually greatly exaggerate harms of diet products).

"Liver transplant!!!!" Please. Brand new foods she'd probably love is turkey and modern chicken. Turkey is a New World bird, selling them at Medieval Fairs is a complete anachronism. The only birds they ate were tiny pigeon-like birds.

As far as health- she would have grown up with no antibiotics, no immunization shots, total ignorance of germ theory, people throwing their waste out the window because of no plumbing, unsanitary cooking conditions everywhere. Water was often contaminated, often being too close to farm animal waste. No showers or warm baths for anyone bu royalty. I think such a sturdy specimen would do great with the additional benefits of modern medicine and sanitation. Maybe she's be more susceptible to modern minor colds, but she may have grown up constantly fighting minor colds and flu, anyways.

  • $\begingroup$ It's true that our diet is stunningly different from that era: we eat staggeringly, incomprehensibly, more carbohydrates. $\endgroup$ – Fattie Jan 29 '18 at 1:34
  • $\begingroup$ Common people for sure, but royalty and aristocrats? Peasants of course. What about their "daily bread" as referred to in the Bible? They had more wine and alcoholic drinks, because it was safer to drink than water, which was easily contaminated. We also have models and anorexics. $\endgroup$ – Cuvtixo Jan 30 '18 at 6:19
  • $\begingroup$ Yeah, we eat incomprehensibly more carbohydrates than 1200s Europeans. Recall too the overwhelming addictive substance everyone alive today lives on, coffee, did not exist then. The rich in Europe ate Sugar by 1500, but sugar really only existed as we know it since 1800. (And too, modern "industrial era" degermed flour is the other incredible change.) I really appreciate you're pointing out the quote from our colleague is a dramatization! :) But someone arriving here from the pre-carb era, into today's "carb era", that is the huge change they'd find - carbs N coffee. $\endgroup$ – Fattie Jan 30 '18 at 13:28

I don't think the biological environment of 2018 would be lethal to her, if she gets with normal preventive care (e.g. vaccines)... but unwanted government attention could result in a fate that's worse depending on how the government feels about time travel.

Big problem: she's stateless. A lot of nations have nationalized or single-payer healthcare, which means a person who's not in the system, or who has never had any of these vaccines, will be very, very unusual, and will raise a lot of questions by a lot of people.

They would really dig into how she could possibly have been missed by the health system, out of a loving desire to stop others from being missed,vand to justify the cost (to the government) of the full regimen. That would only raise even more questions, which would escalate and come to notice of officials less interested in her welfare.

Stateless means is an illegal alien in every country in the world, and a citizen in none. It would be a challenge to establish a nationality for her. Each of these ideas requires her looks fit the story. Might be hard for an Irish woman.

  • Find a country whose records for citizens of that age are very poor due to extended civil disorder, and for which it would be common for an adult woman to just pop up with no records whatsoever. Assimilate enough to pass as a native and ask for the now-stable government to document you.
  • Join one of the streams of refugees somewhere around the world, after assimilating enough to pass as one.
  • find a country that has path to citizenship for illegals who arrived as children, e.g. USA DREAM Act.
  • Fabricate some sort of "Kimmy Schmidt" style story where she was born in captivity of some creepo.
  • Convince a relevant government that her parents were "off grid" freaks who didn't register her birth or do any of the usual government things. Pass a DNA test that proves definitively that she's from around here.
  • Game immigration laws like those of the UK where they can only deport a person if they can prove their original citizenship (which they'll never find for her). But "permanent limbo" isn't a very good existence.
  • Game the programs some countries have to help stateless people.
  • Be hugely political to curry favor of a semicorrupt country like Russia whose leaders freely hand out citizenships to buddies.
  • time travel to when time travel is a normal thing, and "land" (clear immigration) in the normal way.** If you're coming from the past, get a lawyer. Thanks Pere.

And then you could get on their national health system and get your care, because these things would quiet the question of why her history is a black hole and why she's never had a vaccine.

Another option is go to a country where the medicine is quite good, but very disorganized, balkanied and inefficient (and they like it that way). Where it's rather common for an anonymous person to walk into an urgent-care with no identity or insurance documents whatsoever and ask for a-la-carte care and peel off $20 bills to pay for it. I'm speaking of course of the United States. Doctor's offices keep their own medical records and don't share unless asked by another office. You could keep your own medical records and get 100 vaccines at 100 urgent care's or free clinics. There, the risk is missing an important vaccine.

** my greatest aspiration is to travel to England, find where Immigration enforcement is working, step out of a blue Police Box that wasn't there before, and go "pardon me, are you with Border Force? Would you mind--" and pull out my passport.

  • $\begingroup$ If you don't make a secret of time travel but there are still no legal provisions about it, she is just a person born in the country some time ago. That would qualify for citizenship or at least residence permission in most countries of the world. $\endgroup$ – Pere Jan 27 '18 at 10:10
  • $\begingroup$ @Pere yeah, she'd be expected to go to immigration immediately in her nation of entry and tick the "time travel" box, and they would land her, provided she has a believable path to leave or seek citizenship somewhere. Then, go to her historical location's immigration and ask her citienship be recognized... she could be interviewed by scholars of the age to confirm that her knowledge and mannerisms match their story, DNA test etc. $\endgroup$ – Harper Jan 27 '18 at 17:23
  • $\begingroup$ It doesn't matter much for immigration because she has just travelled in time, not in space. However, legislation may be different by country. For example, anybody born in the island of Ireland before 2005 has right to Irish citizenship, and therefore if the story is set in Ireland she is not going to have any trouble with her paperwork. $\endgroup$ – Pere Jan 27 '18 at 17:47
  • $\begingroup$ @Pere That's my Doctor Who bias showing, I was assuming all time travel machines can also travel in space, not least so they don't land 30 feet above or below the ground when they arrive in the new time. I agree it shouldn't, and maybe it won't if time travel is normalized. Otherwise, even in the wild US, a 30yo who just walks into a government office and claims they're a citizen who has never been documented, will have a rough go of it., and would be assumed to be a DREAMer. $\endgroup$ – Harper Jan 27 '18 at 18:00
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    $\begingroup$ Yes, even if time travel is not a secret, the issue is very likely to end in court, with a judge ruling where was she born and what means being born in the country in a time when the country didn't exist or had different borders. $\endgroup$ – Pere Jan 27 '18 at 18:36

He should take her to the doctor to get the standard vaccinations everyone gets. These are also given to people who move to a new country.

If she gets sick, he should take her to the doctor, as you would with any other person. If bacterial infections become an issue, she will likely be prescribed antibiotics. That will likely render your concern moot.

Possibly he might want to watch her diet and put her on an exercise program, since the drastic change in lifestyle may lead to unhealthy habits, which are also common to non-time travelers. But an upper class person like a princess is probably already aware of the basic concepts.

The bigger issues would probably be social: Friction due to unfamiliarity with contemporary culture (not very different from the average immigrant I imagine) and issues with paperwork (in most places he could probably resolve it by marrying her). Also, leaving behind your home, family, friends and everything you know forever isn't very pleasant - but then again, it was not something unheard of for people in the past (especially princesses who could be married off to kings of distant lands) so even that might not be as big a shock.

Would her immune system ever adapt to modern bacteria or is she doomed to suffer a dark fate?

Yes, the immune system has an adaptive component. It can acquire immunity by raising antibody repertoires against new pathogens it encounters, even if they were not "hardcoded in". This is how vaccines work.


Yes, but not for the reasons you're thinking

You travel back in time carrying all sorts of bacteria you're immune to. Assuming this isn't a 'smash and grab' sort of time travel abduction then you go back carrying the seeds of diseases which have been fighting off modern medicine for years, things that have evolved to combat everything from our early 'cures' up to the modern day antibiotics we're worried about becoming obsolete in the modern day.

You're taking these back and giving them an extra 800 year incubation period in a civilisation which hasn't evolved their weapons of warfare along side them. We couldn't assume the society you return to would be anything like the one you left. 800 years of new deaths changes the make up of the modern day population quite drastically (assuming you travel and meet a few people who trade and can carry the diseases).


Bacteria aren't that big an issue, unless she contracts MRSA in which case she's just as screwed as any modern human, she's probably better at dealing with bacteria than we are as she's been exposed to a lot more of it. The biggest threat is going to be viral, in particular she will effectively be a virgin field when it comes to the modern cold and flu, your traveller could vaccinate her against this but if he doesn't get her protected soon enough...

  • $\begingroup$ Humans had to deal with viruses in the past too. The immune system adapts to all dangers if it is not overwhelmed at once. I would say that vaccination would be the worst that could be done to her, she has had all the childhood diseases and is pretty permanently immunised against them instead of the somewhat limited results most of us have from vaccinations. People who contract Measles as a child don't need a booster shot :-) $\endgroup$ – KalleMP Jan 28 '18 at 20:23
  • $\begingroup$ @KalleMP If she doesn't get a vaccination against modern, post-1918, flu strains she's in deep trouble, it's the only thing I can think of that would warrant such precautions and I would suggest that she only get it once after that she's prepared to fight off next year's set reasonably well. $\endgroup$ – Ash Jan 29 '18 at 10:55
  • $\begingroup$ A brand new baby is not automatically vaccinated with this years virus strains any more than you are, though they do get some antibody coverage from mothers milk (when available). However these antibodies are there to allow the baby to fight off current infections before their own immune system is up to speed. After the child's immune system is working fully from 6 months and up it starts to create its own antibodies in response to external infection vectors (or vaccines). An adult has a working immune response that fights new intruders every year in 1200 or 2012. $\endgroup$ – KalleMP Jan 29 '18 at 11:30
  • $\begingroup$ @KalleMP Virgin Field, an individual from 1200 is effectively a new born, actually they're a good deal worse off (they have no genetically inherited defense unlike a descendant of a Spanish Flu survivor), when it comes to the modern strains of fast mutating viruses like influenza and the common cold, as such she needs some protection while she gets up to speed or they'll kill her. For reference see what European diseases did to the population of the America's when they made first contact. $\endgroup$ – Ash Jan 29 '18 at 11:47
  • $\begingroup$ The genetic defence is valid. The epidemics were bad because the populations had no previous exposure so everyone was a virgin field and had herd susceptibility (deliberate heavy exposure may have been the case at times as well). The locals had no experience with or treatments for the diseases. The 1200 lady would have to fight off one or two strains at a time with an adult immune system and modern medicine available in the case of complications. I believe that giving her vaccines from the future would compromise her more and to quote, "First do no harm." $\endgroup$ – KalleMP Feb 1 '18 at 8:07

In order for her to survive in the 1200s she would need to have a very strong immune system. There wasn't a lot of good medicine available in those days so it was difficult for the weak to survive. That would be advantageous when she came to the 2000s. She would more than likely have a strong immune system. However she would still get infected easily with bacteria and viruses that she is not accustomed to, may get sick a few times. She would need to get the same vaccines as a child.

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    $\begingroup$ Welcome to WorldBuilding Johnny! If you have a moment please take the tour and visit the help center to learn more about the site. Have fun! $\endgroup$ – Secespitus Jan 29 '18 at 13:19

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