On another forum discussing a recent time travel movie, a question arose of whether the protagonist, who travelled to 1929, would have been more at risk for disease than in his native time, and also whether he presented a great risk to his peers in 1929. Someone also made the claim that blood changes in the population over decades mean that someone who is O+ in our time won’t be compatible with a donor too far in the past.
Is this true about blood donations? And how would a modern person fare with risk of disease 50, 100, 500, 1000 years ago? How much would he put others at risk? I imagine the immunization shots we get would make us immune to many of the big killers like Polio. Would immunization shots prevent us from passing on those same diseases? Are there other diseases we carry but are effectively immune to naturally that would harm past peoples? I also wonder how much the general lack of hygiene is times gone by would factor into our susceptibility. Would having greater hygiene protect us, or would everyone else’s bad hygiene weaken the effects of our own good hygiene?
I imagine that if a modern time traveler (younger than, say, 40 years old) were to go back to the 1960s or earlier, they’d be at real risk of smallpox. The general population has not been vaccinated for smallpox in the US (except for special cases) in almost 40 years, if not longer. But that’s not because we’ve evolved some type of defense against it. Rather, it’s because we’ve pretty much eradicated smallpox almost worldwide. If an unvaccinated person went back in time to a period when smallpox was still at large, they’d be susceptible.
I don’t recall hearing of a lot of cases of smallpox in the US in the '60s, so I doubt our time traveler would be at risk from that. I was sensitive to this stuff even at 10, since I got a zillion vaccinations before I went to Africa in 1961.
I’d worry more about flu, especially if you went back to 1917 - 1918. I assume that since we are descended from survivors we might have slightly more immunity, but probably not enough. I’d also worry about things in drinking water that have now been reduced or eliminated by better sanitation.
“The global eradication of smallpox was certified, based on intense verification activities in countries, by a commission of eminent scientists in December 1979 and subsequently endorsed by the World Health Assembly in 1980.”
Of course this statement depends upon the time travelled to, but using the numbers thrown out by the OP and others in this thread; 1929 and the 1960’s, possibly not nearly as much as you might suspect.
“It is likely that HIV first appeared in humans in Africa in the 1930’s or 40’s as a result of infection by simian immunodeficiency virus (SIV) from chimpanzees.”
Of course, if you gave it to just the right IV drug user at just the right time… sure, but the time periods that have appeared in this thread do not massively predate when there was apparent human disease burden with HIV.