With the COVID-19 vaccine rollout gearing up across the globe, expectations are rising for the restart of international travel. And so that travelers can move safely from one country to another without spreading the virus, Japan and other nations are looking to introduce a system of vaccine passports.

On Tuesday, the European Commission proposed a Digital Green Certificate system that will show if a person has been vaccinated against COVID-19, received a negative test result or recovered from COVID-19. The U.S. and the U.K. are also looking into similar systems.

But with delayed vaccine rollouts and uncertainties about problems that might emerge once a global vaccine passport system is in place, Japan remains cautious about this approach.