> I have never once seen a Japanese traveler required to produce any medical paperwork along with their passport (and I have flown a lot between both countries).
That's because a significant number of countries that require vaccines also require something called a "visa."
Visas have many years of history, and they're generally obtained beforehand. When applying for visas, you submit various documentation, pay a fee, and it makes your entry process much easier. When traveling first world to first world, visa checks for travel are generally waived. Going first world to anywhere not-first world, or in the opposite direction, usually requires some degree of a visa process.
That's because a significant number of countries that require vaccines also require something called a "visa."
Visas have many years of history, and they're generally obtained beforehand. When applying for visas, you submit various documentation, pay a fee, and it makes your entry process much easier. When traveling first world to first world, visa checks for travel are generally waived. Going first world to anywhere not-first world, or in the opposite direction, usually requires some degree of a visa process.