But what if they fly to a country with a resistant mutation, bring it back here, and then your vaccine does nothing?
Vaccine passports for travelling to other countries that have low vaccination rates makes sense - to protect those in other countries that haven't been vaccinated.
But as vaccine resistant mutations don't actually exist so far, then really no point in having policies in place that pretend they do. Just get the vaccine manufacturers to work on updates to deal with them. Which they are.