CDC Director, Dr. Rochelle Walensky admits that that the vaccines don't stop the transmission of covid, they just reduce the severity of covid in the person who takes the vaccine, you can still get infected with covid and be asymptomatic and unknowingly spread the virus to others. Here is the clip of her being interviewed on CNN: https://mobile.twitter.com/cnnsitroom/status/1423422301882748929
She is basically saying that the vaccinated are about as likely to carry the virus as the unvaccinated and being vaccinated doesn't make you exempt from covid protocols, that's why testing for both the unvaccinated and vaccinated are still in place.
And besides, many fully vaccinated nations that have vaccine passport systems had a high surge of covid cases, the majority of those cases being in the fully vaccinated than the unvaccinated.