European Union leaders have vowed to accelerate the rollout of Covid-19 vaccines as concern mounts about the spread of new variants of the virus.

They said that restrictions, including on travel, should remain in place in many parts of the 27-nation bloc.

Covid-19 has killed more than 531,000 people across the EU.

“Our top priority now is speeding up the production and delivery of vaccines and vaccinations,” EU Council President Charles Michel said, adding a warning for vaccine makers: “We want more predictability and transparency to ensure that pharmaceutical companies comply with their commitments.”

The European Commission has sealed deals with several companies for well over 2 billion vaccine shots — far more than the EU population of around 450 million — but only three have been authorised: jabs from Pfizer-BioNTech, Moderna and AstraZeneca.

Virus Outbreak Europe Summit
Charles Michel, right, and European Commission President Ursula von der Leyen participate in a media conference (Olivier Hoslet, Pool via AP)

Officials say the Johnson & Johnson vaccine could be approved next month.

But some senior officials at the big pharmaceutical companies, a few of whom were grilled by EU lawmakers not far from where Mr Michel was chairing the video-conference summit in Brussels, said it is no simple matter to build new vaccine production sites.

Moderna CEO Stephane Bancel said production problems are inevitable as companies work around the clock to do in one year what normally takes up to four years. Most of the company chiefs said they expect an improvement in the second quarter.

“Every time there is a human error, equipment breaking down… or raw material from one of our suppliers late by a day, you cannot start making the product because it will not be safe, you will not have the right quality,” Mr Bancel said, explaining the technological issues facing producers.

AstraZeneca CEO Pascal Soriot said a big challenge is to improve yield — the number of doses that can be extracted from a litre of vaccine.

He also rejected the idea that companies can simply open new production sites to solve the problem, saying that engineers must spend a lot of time training staff.

“Our teams are absolutely stretched to the maximum. There’s no way they could train any more people,” he said, and insisted that most companies developing vaccines probably face the same constraint.

Mr Soriot came under fire after he confirmed that the company would deliver less than half the vaccines it had committed to in the first quarter.

The EU has partly blamed supply delays for lagging behind nations like Israel, the United States and Britain when it comes to vaccinations. By early this week, 6.5% of the adults living in the EU had been vaccinated, compared to more than 27% in the UK.

Mr Soriot said AstraZeneca would deliver 40 million doses to the EU in the first quarter, attributing the delay to complicated production issues, including “lower than expected output in our dedicated European supply chain”.

European Commission President Ursula von der Leyen noted pointedly that in terms of companies honouring the delivery commitments in their contracts with Europe, “there is room for improvement” at AstraZeneca.

Still, despite the slow vaccine rollout in Europe, Ms Von der Leyen said the bloc still aims to inoculate 70% of all adults — around 255 million people — by September.

“This is a goal that we are confident we will reach,” she said.

Border checks remain a sore point.

Divisions among EU member countries, including Germany, Austria, Belgium and the Czech Republic, on restrictions to stave off transmission has again raised the spectre of travel delays and long traffic queues in a bloc that prides itself on being a seamless market.

Mr Michel told reporters that “non-essential travel may still need to be restricted, but measures should be proportionate”.