All EU member states are expected to have signed up by July to ensure seamless COVID-free travel across the continent.
Sixteen countries have begun using the EU's 'Digital COVID certificate' (EUDCC) to enable their citizens to easily travel across the bloc.
The European Commission says fifteen member states - Austria, Belgium, Bulgaria, Croatia, Czech Republic, Denmark, Estonia, Germany, Greece, Latvia, Lithuania, Luxembourg, Poland, Portugal and Spain - have connected to the gateway and started issuing the first certificates.
They are joined by Iceland, which is the first of four European Economic Area countries to join the scheme.
Formerly referred to as the EU Digital Green Certificate, others will be expected to follow suit when its functions are deployed continent-wide by the 1st of July.
The certificate is available in digital or paper form and is free of charge. The gateway allows for all certificates' QR codes to be accessed.
The EU's plan is for a single system to facilitate safe travel by verifying the pass holder's coronavirus status – whether through vaccination, a recent negative test result, or proof of recovery from the virus.
More than 20 countries have successfully tested the system in the last month, the European Commission says. The launch follows an agreement between the European Parliament and Council on regulation.
The certificate was formally enshrined in EU law in a record 62 days on the 14th of June after a significant majority vote from the European Parliament.
Alberto Alemanno, Professor of EU law policy at HEC Paris, tells Euronews the system would put cooperation between EU countries to the test as many have looked to enforce their own rules on movement amid the pandemic.
"We need to remember that the conditions of access to get this certificate will change from one country to another. It is each country to determine who gets the vaccine, who gets the test... who is going to be declared as immunised," he says.
"Each country reserves the right to refuse the COVID certificate as such. This might actually be the source of much confusion and unpredictability."
The European Commission is aiming for 70 per cent of the bloc's 450 million residents to have received at least one dose of the vaccine by late July.
Commission chief Ursula von der Leyen revealed last month that the EU is on track to reach that target with more than 250 million doses administered so far. More than 80 million Europeans have already been fully vaccinated.
Brussels has also previously indicated that fully-vaccinated people from countries outside of the EU should be able to visit with no quarantine requirement - provided they were administered EU-approved jabs.
The European watchdog has approved the use of four vaccines: Pfizer/BioNTech, AstraZeneca/Oxford University, Moderna, and Johnson & Johnson.
According to Our World In Data, more than 38 per cent of the EU's population has received at least one dose of the vaccines, compared to 50.3 per cent in the US, 57.7 per cent in Canada, 58.1 per cent in the UK, and 63 per cent in Israel.