I've not been 100% well today so have rested up and looked at books and read things online.  Anyway, on a (non-history) forum there was some discussion about the value (or not) of "Covid passports" and whether or not the introduction of them would impinge on individual freedom.  Someone from the USA or Canada (I think) said surely passports already have vaccinations marked on them but was informed that UK ones don't. I was ignorant of the fact that some countries do carry information about which vaccinations the bearer has received.

If I understand rightly a "Covid passport" isn't a passport as such but a certificate of vaccination and may be intended (if they come to fruition) for "internal", domestic UK use.  From looking at NHS information on the web some countries want an International Certificate of Vaccination or Prophylaxis (ICVP) to be shown if a person is entering or leaving a country (for yellow fever or polio for example per the NHS).  With Covid-19 I suppose things would depend on the rules in force in the destination country.

I have a vague recollection of mention of internal passports being used in France, or at least some parts of France, historically.  My knowledge of the history of passports is sparse.  There's always Wikipedia I guess.