Lisbon, Jun 17 (IANS): The Portuguese health authorities began to issue the EU (European Union) Digital Covid Certificate on Wednesday, which will allow free transit in the bloc's 27 member countries as well as Iceland, Liechtenstein, Norway, and Switzerland.

According to the authorities, the so-called "Covid-19 passport" will be granted to those who have already been vaccinated, recovered from the disease, and those who present a negative result in polymerase chain reaction (PCR) tests.

The Certificate can be requested and received over the internet free of charge for Portuguese residents. It's also available through a smartphone application integrated with other EU countries, the Xinhua news agency reported.

President of the European Commission Ursula von der Leyen, on her visit to Portugal on Wednesday, was the first to publicly test the system.

"I am now starting my tour of the 27 Member States within the framework of 'NextGenerationEU', our recovery and resilience plan, and I am very curious to test and see how this certificate works," she said, adding that the system is already in use in 15 member states.

Portugal has administered at least 6.96 million doses of Covid-19 vaccines so far, according to the health authorities.

As the world is struggling to contain the pandemic, vaccination is underway in an increasing number of countries with the already-authorised coronavirus vaccines.

A total of 287 candidate vaccines are still being developed worldwide -- 102 of them in clinical trials -- in countries including Germany, China, Russia, Britain, and the US, according to information released by the World Health Organization on June 15.