I've been searching through some boxes looking for something and have realized I used to write a hellofalotta notes about writing. Think like bits of conversation, ideas, plot lines, etc. And I don't do that as often as I use to. So let me share this gem.
Time travelers would be subject to infectious diseases that their immune systems are not prepared to handle. Would then need a series of vaccines? Would doctors know what to inoculate them with? Or could they bring back to their future time a plague that would wipe out large portions of their population leading to political will to never time travel again, or societal collapse leading them to never be able to time travel again?