European Union leaders are set to agree on Thursday to work on certificates of vaccination for EU citizens who have had an anti-coronavirus shot, as southern EU countries that rely heavily on tourism are desperate to resurrect this summer’s holiday season.

Restriction and lockdowns to curb the spread of the virus prompted the deepest ever economic recession in the 27-nation bloc last year, hitting the south of the EU, where economies are often much more dependent on visitors, disproportionately hard.

With the rollout of vaccines against COVID-19 now gathering pace, some governments, like those of Greece and Spain, are calling for a swift adoption of an EU-wide certificate for those already vaccinated so that people can travel again.

But while EU members agree a vaccination certificate would be welcome, work is needed on the details, including whether it should be in digital form, be accepted globally and at what stage of the 2-step inoculation process it should be issued.

“We call for work to continue on a common approach to vaccination certificates,” said a draft statement of the leaders’ video-conference seen by Reuters, without setting a time-frame for a result.

The EU is working with the International Air Transport Association, which is adamant on reviving air travel, as well as with the World Health Organization and the Organization for Economic Cooperation and Development, officials reported.

Officials said however that travel with certificates also raised legal questions because those last in line for vaccinations could argue their freedom of movement was unfairly limited by the often months-long queues.

EU officials also say there is no guidance yet from the WHO and EU agencies whether people who have received two shots of the COVID-19 vaccine can still carry the virus and infect others, even if no longer vulnerable themselves.

It was also not clear if people could be infectious having already fought off the COVID-19 themselves, for how long they remained immune and if they too should get certificates.

Nonetheless, time is short for countries in the south, where the hospitality sector needs to know what it should prepare for in the coming months.

Earlier this month, Greece and Israel signed a deal to ease travel restrictions to Greece for Israelis with proof of vaccination.