The EU's Digital COVID certificate officially comes into force from today, 1 July.
By Wednesday evening, 21 EU nations, out of the total 27, were connected to the system's network and 6 others were technically ready. Some countries already began using the new health certificate in June.
According to the European Commission, all member states should now be in a position to issue and accept the pass, except for Ireland which has been delayed by cyber attacks.
A gradual implementation period is now in place, with a grace period running until 12 August for countries not ready on 1 July. During this period, other states should accept national documents on condition they contain data required at a European level.
But the launch comes under the cloud of the Delta variant, which is already prompting EU countries to restrict travel from countries where it is prevalent, such as the UK, Portugal and India.
The airline industry has also warned that EU countries are not coordinating their approaches to vaccine certification, potentially causing long delays at airports during the busy summer season.
What is the EUDCC and how does it work?
Previously called the Digital Green Certificate, the EUDCC aims to allow Europeans to travel easily between the 27 member states. It will be available in some non-EU countries, too.
It consists of information about an individual's vaccination status, test results or recovery status from COVID-19.
Presented as a QR code, the traveller can choose to carry either a digital or paper certificate.
The EU Digital COVID certificate (EUDCC), as it is officially known, is free and should be recognised by all 27 EU countries as well as Switzerland, Liechtenstein, Iceland and Norway.
The EU is in talks with several other countries, such as the United Kingdom and the United States, over mutual recognition and operation of COVID-related documents.
The pass applies in three situations: it attests whether a person has been vaccinated against COVID-19, whether they have had a recent negative test, or whether they are considered immune having previously contracted the disease. Proof of a positive PCR test will be needed.
Countries are obliged to accept vaccines approved by the European Medicines Agency (EMA): Pfizer/BioNTech, Moderna, AstraZeneca and Johnson&Johnson.
They can also, though it is not compulsory, also admit people inoculated with vaccines authorised in some EU countries, such as the Russian Sputnik V in Hungary, or with products approved by the World Health Organisation (WHO), such as the Chinese Sinopharm.
The certificate is supposed to do away with the need for a supplementary test or quarantine upon arrival in another country. However it is still possible for a member state to introduce restrictions if the sanitary situation of the country or the region the traveller has come from is deteriorating.
In this case the destination country should try to inform the Commission and other EU countries 48 hours before restrictions come into force.
Concerns from the airline industry
Europe's air travel industry warned earlier this week that the EU's plans for a digital COVID certificate were still "fragmented".
Groups representing the continent’s largest airlines and airports have expressed fresh concerns that there will be long queues for travellers unless countries better coordinate the rollout of the certificate.
The letter of warning to EU leaders was signed by airports group ACI Europe, as well as airlines representative bodies A4E, IATA and ERA.
"Certificate verification will undermine smooth summer travel for EU passengers," they said in a joint statement. "As passenger traffic increases in the coming weeks, the risk of chaos at European Airports is real."
"Duplicate checks and lack of verification tools provided to airlines will cause unnecessary airport queues and longer processing times if not addressed by the Member States."