British Airways Embraer 190 aircraft takes off from London City Airport. | JOHN SIBLEY

The European Union aims to introduce a central system in June to record citizens' COVID-19 vaccines, tests and recovery to help them travel across the 27-nation bloc and open up summer tourism.

While the EU is still discussing how exactly to use this system, here is how it would work technically, based on comments by officials with the EU executive and two German firms involved -- Deutsche Telekom unit T-Systems and software maker SAP.

· A COVID certificate would be handed out for free by health authorities in EU countries to people who received a vaccine, had a negative test or are immune, having recovered from COVID.

· The certificate could be a paper or a digital document, with a QR code carrying encoded data that would be uploaded to the central system to allow verification in other EU countries through a single gateway.

· EU countries can link their national vaccine records to the central one using a template provided by the German developers.

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· The companies would also roll out wallet apps for storing certificates on individual mobile phones, and a verification app that would flash green, if it scans a valid certificate, or red otherwise.

· A dry run is due to start next month involving more than a dozen EU countries including France and Spain, while a full rollout of the system in all member states is planned in June.

· EU countries would also be able to issue certificates for those who have already received their shots.

· Linking up foreign countries to the system is technically possible if a political agreement is sealed and an equivalence decision granted by the EU to share data.

Diplomats said this week the likely result of the EU's efforts is that certificates would be used as a minimum common denominator, while leaving much leeway to each country on what rights they would be willing to grant to holders of such passes.