Even as the COVID-19 pandemic continues to rage in many corners of the world, places that have successfully vaccinated a substantial share of the population are plotting the next step: how to let people start traveling again, whether for beach vacations or board meetings.

By early summer, countries of the European Union and beyond aim to issue vaccine passports that would let those who have been inoculated freely cross borders.

Some places — Australia and New Zealand, for instance, and Singapore and Hong Kong — are joining together to create "travel bubbles” that allow citizens to visit without mandatory quarantines. And governments are drawing up lists of vaccines and tests they deem sufficiently effective to permit entry.