In reply to tom_in_edinburgh:
> Do they need to change the Yellow Fever jab every 9 months?
> Are there about 10 different jabs in use and wildly different rules about gaps between doses.
> They are going to need a techy system if they do this because the situation is complex and in flux and they will need to redefine the rules on-the-fly as some vaccines become ineffective.
> A techy system for travel would probably combine vaccination with multiple other criteria such as a recent negative test.
I have a paper "Health Passport" or "International Certificate of Vaccination. For each type of vaccination (Typhoid, Polio, Tetanus, various Hepatitis, Yellow Fever, etc) it has a box for date given, signature and status of vaccinator, type and batch no of vaccine, date it is effective until and official stamp of vaccinating body. That's a non-techy solution that has worked for me since 1974. OK, it's possibly easy to forge entries, if you're that way inclined, but I've had no issues with being able to keep things up to date. The type and batch no would cross-index to vaccines that have become ineffective.
For the last 3 years I've had a "MyGP" app on my phone, which contains all my basic medical records, including all the vaccinations I've had back to 1995, plus the results of all the blood tests I've had since then, too. A more techy solution, but when I was travelling before lockdown, the developing countries I visited put far more store in my paper ICV than in my phone app.