If you've already been vaccinated, you can travel to certain countries, but you may still be required to quarantine or show a negative PRC test. Travelers must be fully vaccinated, with the final dose (or a single dose, for one-jab vaccines like Johnson & Johnson) administered at least 14 days before departure. Certain countries (such as France and the EU) are thinking of releasing a special vaccine certificate to allow vaccinated people to travel freely, but this has not been finalized yet.