German Chancellor Angela Merkel has defended the EU's decision to procure coronavirus vaccines jointly as the bloc struggles with delays in rollout.
EU leaders are holding virtual talks to discuss vaccine supplies and improving distribution across the 27 nations.
Pressure is mounting upon them to deliver after other countries, like the UK, achieved much faster vaccination.
The European Commission is seeking added controls on vaccine exports.
Such controls could affect supply to the UK, where Prime Minister Boris Johnson has warned against imposing "blockades".
European Commission head Ursula von der Leyen tweeted that the summit would "ensure that Europeans get their fair share of vaccines"
A third wave of coronavirus infections is sweeping across much of mainland Europe.
EU states have seen some of the deadliest outbreaks of the pandemic, with Italy recording more than 106,000 deaths, France 93,000, Germany 75,000 and Spain 73,000.
Yet recent figures show just 12.9 doses of vaccine have been administered per 100 people in the EU compared with 44.7 in the UK and 37.2 in the US.
The European Commission has blamed pharmaceutical companies - primarily AstraZeneca - for not delivering the promised doses to the EU. The company denies that it is failing to honour its contract with the EU.
A site in Belgium produces the Oxford-AstraZeneca vaccine, and another in the Netherlands is expected to increase supplies of the jab in the EU.
Brussels has said that of the more than 40 million doses exported from the EU over the past two months, a quarter were sent to the UK.
The UK and the EU said on Wednesday they wanted to "create a win-win situation and expand vaccine supply for all".
In another development, Denmark suspended use of the Oxford-AstraZeneca jab by a further three weeks, saying it was still looking at a possible link to blood clots despite the European Medicines Agency's recommendation to use the vaccine last week.
What did Merkel say?
Speaking to German MPs before the summit, the German chancellor said that if some members had had vaccine supplies and other had not, it would have shaken the EU's internal market to its core.
But some EU states, led by Austria, are calling for a revision in the distribution method after failing to obtain enough doses earlier this year.
"We are in a situation where some member states will have vaccinated their population by the beginning or middle of May while for others, it will take six, eight or ten weeks longer," Austrian Chancellor Sebastian Kurz said last week.
Mrs Merkel warned that the impact of the pandemic could go beyond "far beyond this year".
The EU, she said, relied on what vaccines it could make locally because "British production sites are manufacturing for Britain and the United States is not exporting".
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EU leaders had planned to meet face to face in Brussels but a third wave of the pandemic is sweeping across much of mainland Europe. So, a summit by video-conference was deemed safer.
EU politicians are under increasing public pressure. Many voters blame their governments and Brussels for a vaccine rollout that lags far behind the UK.
The European Commission blames pharmaceutical companies - primarily AstraZeneca - for not delivering jabs promised to the EU.
But leaders are divided over proposals for new restrictions on vaccine exports out of the bloc to boost domestic supply. Some fear that would disrupt global supply chains needed to manufacture vaccines and damage already strained relations with the UK after Brexit.