I hear people saying that a vaccination passport will be paramount to enable resuming international travel.
AFAIK, it is not at all clear that a vaccination will make people not contagious. (nature)
Covid19 vaccines helps not getting the covid19 disease, it doesn’t imply that people is not going to be contagious.
If you are a vaccinated person travelling to the UK, the vaccination passport only tells the UK administration that you are not going to cause burden onto the NHS (National Health Service).
As we will be more and more vaccinated, to resume travelling, we will need to strenghten the capacity of PCR testing (swabs).
With swabs certifications we can show that, up to 2 days before, we were not contagious, thereby minimizing the probability of contagion.