Joe Schmo is your average college graduate who is suddenly transported back to medieval times, without time to prepare. From there the stories, and questions on this site, are all about how he can use his technological knowledge to change mankind. That assumes he survives long enough though...

Would Joe be able to survive the diseases and viruses of the time period? People from the US can't even drink water in Mexico because we are so dependent on our filtration, I can't imagine medieval water to be any cleaner. Would his immune system be able to handle the sudden influx of every-day diseases of the time which he has never been exposed to or developed an immunity to?

He would have vaccinations against some of the biggest killers, which is useful, but what about all the diseases he wasn't vaccinated against?

Now lets assume that Joe is smart, with a general high school and college bachelor's education. What can he do to protect himself? Would he have to start boiling all water before drinking it, until he can slowly build up a tolerance to their diseases?

  • $\begingroup$ Amusing and related video from glove and boots (but not enough for an answer): youtu.be/75nBenOWul0 $\endgroup$
    – PipperChip
    Mar 31 '15 at 16:25
  • $\begingroup$ Does he have access to a supply of antibiotics? $\endgroup$ Jul 21 '15 at 21:11
  • $\begingroup$ @DougWarren assume no. he wasn't planning the trip, didn't get to protect himself by vaccination or bringing modern medicine. $\endgroup$
    – dsollen
    Jul 22 '15 at 14:27
  • $\begingroup$ Has anyone thought about the danger of infecting medieval peeps? $\endgroup$
    – Nick Dzink
    Aug 29 '17 at 23:27
  • $\begingroup$ @NickDzink That's crazy talk! Who would want to infect adorable marshmallow chickens, even if they were midieval!? It actually is an interesting point, though I don't know how large the risk is. I imagine were not carriers for as many diseases as people of the past, as we relay on medicine to destroy the disease entirely instead of letting our puny body try to figure out a parital defense. A single person who is less likely to be a carrier of many diseases probably isn't that high an infection vector? $\endgroup$
    – dsollen
    Aug 30 '17 at 13:36

Well when he arrives, his health should be much better than the majority of the population where he lands. But yes, he'll have to be careful what he drinks. That is one of the reasons many drank wine, beer and grog, though they didn't know why it was 'healthier'.

Probably the biggest disease he'll have to worry about that he won't have immunization against is the Black Plague, it's deadly and spreads quickly. A saving grace would be knowing it is spread by rats and fleas. Good clean hygiene is the best prevention there.

He will also have to learn to lie about where he gets all his knowledge from, people were/are superstitious and surprising scientific phenomena practiced well could stir rumors of witchcraft and that never ends well for the accused.

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    $\begingroup$ You might overplay the "witchcraft" and "never ends well for the accused" thing. While it was real, it is overly exaggerated today. Imagine if someone in 2615 says that in the year 2015 flying was so dangerous that every airliner was constantly in grave danger of just dropping down. Only around 2%-3% of the people judged by the inquisition were sentenced to death, the majority was declared "not guilty". Also, there are many reports of healers, both real and quacks, attributing their works to skill or divine intervention, so the "healer = witchcraft" theory doesn't have any good foundation. $\endgroup$
    – vsz
    Mar 31 '15 at 15:48
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    $\begingroup$ @vsz true, but being a 'foreigner' who can barely be understood, performing miracles would still be dangerous. $\endgroup$
    – bowlturner
    Mar 31 '15 at 15:55
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    $\begingroup$ I would say that, generally speaking, the most dangerous illness will not be the plague (unless he lands in the middle of an infested town), but smallpox. Also, some influenza were quite nasty, but killed mainly the weaker population (and as you said, the time traveller should be way better than most of the population). $\endgroup$
    – SJuan76
    Mar 31 '15 at 18:42
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    $\begingroup$ @SJuan76 but isn't small pox something most of us have been inoculated for? $\endgroup$
    – bowlturner
    Mar 31 '15 at 18:48
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    $\begingroup$ I have checked (cif. read in Wikipedia) and it seems unlikely. At least in Spain is not in the official scheduled vaccines, and it seems that in the rest of the world it is not, either, with vaccines ready for use only in the case of an outbreak. It makes sense, the vaccine seems to have some risks/side effects and, with smallpox officially eradicated since long ago, seems unlikely that people should afford those for no actual protection (since there is already practically zero chance of getting the disease). $\endgroup$
    – SJuan76
    Mar 31 '15 at 19:04

Yes and no. Funny enough, I thought of this exact same question when I had a childhood fantasy of a modern aircraft carrier group suddenly being teleported into Roman times. Don't ask why.

Anyway, In the modern world, we are no longer vaccinated against things like bubonic plague (since sanitation has made that one go away) and smallpox (since we actually destroyed that one, humanity FTW). You'll have to get your smallpox vaccine fast or else you're screwed, since it is also ridiculously deadly and spreads extremely fast.

You'll want to watch out actively for plague, since contrary to bowlturner's answer— there is mounting evidence that the plague in the 1300s was also spread by air in the form of pneumonic plague instead of bubonic plague.

There's also the matter of things like the 1918 flu, which might kill you really fast by cytokine storm because of our comparatively strong immune systems now. However, most people today are be much better off on that front, since our immune systems are not weakened by chronic childhood malnutrition.

But, other than a few diseases which we might not know of (there have been a few plagues whose cause is not yet determined) and the ones which we already defeated (humanity f*ck yea!), you should be fine in most cases.

However it is, if you want to take such a journey, I don't recommend it. Modern sanitation and medicine is a great thing. Going to the past is basically going to a third-world country without bothering to get vaccines — also known as a bad idea.


Members of the military are vaccinated against plague if there are going to be sent to regions were it is possible that the plague might breakout. I can't count the number of shots I received when I was in the Marine Corps.


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