I realize this might be a shock… But vaccines fail all the time. Their immunity wanes, they cause adverse events and sometimes they spawn rogue strains like what happened with Polio.

BTW we have a case study unfolding real time on restricting people’s travel based on vaccination status. As the COVID-19 vaccine does not prevent transmission, infection or spread, it was a complete disaster. Meanwhile unvaccinated people with natural immunity who don’t spread were unfairly punished for noncompliance.