European Union governments kicked off a debate on Tuesday about how long vaccines are effective against Covid-19 and whether evidence of a booster dose will be required to maintain free travel across the bloc as cases spike.
The executive European Commission is due to present a proposal this week to coordinate free movement using Covid-19 passes, after Austria became the first country in western Europe on Monday to reimpose a lockdown since vaccines were rolled out.
EU coordination on the passes, showing if a holder is fully vaccinated or has a recent negative test or recovery from infection, has allowed an easing of curbs on cross-border travel.
The passes, typically viewed on mobile devices, are issued by individual countries, but are recognised for travel across the bloc. They are now increasingly being deployed in many EU countries for access to indoor areas such as bars or theatres.
Greece has proposed that people should in future only be able to travel freely if they have received a second or third dose in the previous six months and that booster doses should be added to the information shown in EU passes.
Luxembourg Foreign Minister Jean Asselborn said it was vital the 27 EU states agree a common standard. His country would normally receive about 200,000 workers a day from neighbouring countries.
"We can't have different systems in Luxembourg and in Greece, or in Germany or France. It would be against the interests of the European citizens. They demand that of us and it can be done," he told reporters before a meeting of EU counterparts in Brussels.
Irish EU affairs minister Thomas Byrne echoed the view that the EU digital COVID passes, launched in July, needed to continue to facilitate free movement.
German European Affairs Minister Michael Roth said booster doses were now "the order of the day", pointing to scientific studies that show they really bolster immunity. He added: "A digital vaccination certificate is of paramount importance, but it must be based on scientific knowledge."