AstraZeneca’s coronavirus vaccine has been authorised for use in the European Union as a row over its supply continues to rumble on.

The EU is frustrated at supply shortages of the jab and has demanded AstraZeneca doses be sent from British plants to make up for a shortfall.

The European Medicines Agency (EMA) has since licensed the vaccine for use in adults throughout the EU.

Here’s what we know about the dispute between the EU, the UK and AstraZeneca:

– What is the cause of the problem?

AstraZeneca has said initial deliveries to the EU will fall short because of a production glitch – said to be at a hub in Belgium – and it will not be able to meet its supply targets for the first three months of this year.

The Anglo-Swedish company announced initial deliveries in the EU would total approximately 31 million doses, rather than the anticipated 80 million in the first quarter of the year.

With the speed of the UK’s vaccine rollout outstripping other European countries, the EU has suggested doses produced in Europe have been directed elsewhere.

EU Commission president Ursula von der Leyen has now called for an explanation from AstraZeneca for delivery hold-ups, as she insisted the supply orders are “binding” and “the contract is crystal clear”.

– What else has the EU said?EU health commissioner Stella Kyriakides has accused AstraZeneca of a “lack of clarity” and “insufficient explanations”, adding “the answers of the company have not been satisfactory” following a meeting on Monday.

On Friday, the European Commission tightened the rules on the export of vaccine doses produced in the 27 EU countries.

The “vaccine export transparency mechanism″ will be used until the end of March to control vaccine shipments to non-EU countries.

The EU insisted the measure was not an export ban, with officials stating the move was intended to ensure member nations receive the shots they bought from vaccine producers.

European Commission executive vice-president Valdis Dombrovskis told a Brussels press conference: “Today the commission has adopted an implementing regulation making the export of certain products subject to an export authorisation.

“This regulation concerns the transparency and export of Covid-19 vaccines.”

The UK was not named among countries exempted from the new measures.

Meanwhile, the EMA licensed the AstraZeneca vaccine for use in people aged 18 and over throughout the EU.

– Has AstraZeneca responded?

The company’s chief executive Pascal Soriot said the contract only committed to meet the EU’s demands to its “best effort”.

In an interview with Italy’s la Repubblica newspaper that was published on Tuesday, he said the EU’s deliveries were delayed in part because the bloc signed its contract three months later than the UK, and therefore EU manufacturing facilities were still catching up.

Translated by Politico, Mr Soriot reportedly said the “contract is very clear: Our commitment is, I am quoting, ‘our best effort'”.

He explained that AstraZeneca and its partner Oxford University had signed a deal with the UK Government for 100 million doses three months before the EU deal for 400 million doses was agreed.

In response to the EU demanding their doses were shipped concurrently, Mr Soriot suggested it was a “super stretch goal”, and added: “We said, ‘OK, we’re going to do our best, we’re going to try, but we cannot commit contractually because we are three months behind UK’.”

– What has the UK said?

Prime Minister Boris Johnson said this week he is “very confident” about the UK’s vaccine supply, while Cabinet Office minister Michael Gove insisted there “will be no interruption”.

Government vaccine tsar Nadhim Zahawi also said on Tuesday he is “confident” supply of the Pfizer jab – which is produced in Belgium – will continue.

Asked if the EU could prevent Pfizer vaccines from being exported, he told Sky News: “No, I’m confident that the Pfizer vaccine will be delivered.

“Pfizer have made sure that they have always delivered for us.

“They will continue to do so.”

– But will UK supplies be affected?

The majority of the AstraZeneca/Oxford vaccine supply for the UK is manufactured here rather than at the Belgium plant so it is not expected to be disrupted.

The UK is scheduled to receive 3.5 million doses of the Pfizer vaccine over the next three weeks.

Meanwhile, the EU has moved to prevent Northern Ireland from being used as a back door to funnel coronavirus vaccine from the bloc into the rest of the UK.

Stormont First Minister Arlene Foster branded the EU’s triggering of Article 16 of Brexit’s Northern Ireland Protocol to stop unfettered flow of inoculations from the EU into the region an “incredible act of hostility”.

– How many doses of vaccine has the UK ordered?

The UK Government has so far secured 40 million doses of the BioNTech/Pfizer vaccine, 100 million of the Oxford/AstraZeneca jab and 17 million from Moderna – the most recently approved vaccine  -but supplies of it are not expected to arrive until spring.

The UK has also secured 60 million doses of the Novavax jab – to be produced on Teesside – with the hope that the Medicines and Healthcare products Regulatory Agency will approve it for use within weeks.

– How many doses does the UK currently have?

The UK Government has not published figures publicly on how many doses are currently available.

But with First Minister Nicola Sturgeon facing sustained criticism about the vaccination rollout in Scotland seemingly moving at a slower pace than in other parts of the UK – purportedly due to vaccinating higher proportions of care home residents first – she has suggested she could soon reveal supply figures.

Ms Sturgeon said on Thursday: “I think we will just go back to publishing the actual supply figures from next week, so that we all have transparency around that.”

The Scottish Government did – briefly – publish the vaccine doses it had access to, but retracted the documents at the request of the UK Government over apparent concerns about other countries knowing how much is being supplied.

During his visit to Scotland on Thursday, the Prime Minister was asked about the possibility of more data being published.

He said: “We’re in favour of the maximum possible transparency that is compatible with security of supply. That’s the crucial thing, we’ve got to ensure we continue to have national security of supply.”

– How is the rollout progressing in the UK?

As of Thursday, official figures showed 7,447,199 people in the UK had received a first dose of either the Pfizer or AstraZeneca vaccines.