The European Union (EU) has been criticised for the pace of its vaccination programme - 18% of its population has received the jab, compared with 55% in the UK.
The EU rollout has been hit by delays in production and distribution as well as concerns over safety of the Oxford-AstraZeneca vaccine.
Issues with AstraZeneca
In January, the European Medicines Agency (EMA) approved the use of the Oxford-AstraZeneca vaccine for all age groups, but a number of EU countries initially refused to recommend its use for people over 65.
France and Germany eventually revised their stance and approved the vaccine for people aged 65-74 at the beginning of March. But they were among 13 European countries who paused the AstraZeneca rollout again that month - following reports that a small number of people developed blood clots after receiving the jab.
Most countries restarted it after the EMA said there was no evidence that the vaccine caused the clots.
However, on 7 April the EMA said there was a "possible link" between the AstraZeneca vaccine and the clots. The agency concluded that neither age nor gender were a clear risk factor and it is still recommending the jab for all age groups.
Nevertheless, several EU countries, including France, Germany and the Netherlands say only people over 55 or 60 should get the jab, while others like Denmark have suspended the vaccine rollout altogether.
The UK's drugs regulator recommends that people under 30 should be offered an alternative Covid vaccine to the AstraZeneca jab.
The headlines surrounding AstraZeneca have led to a drop in confidence in the jab across the EU. The polling company YouGov reports only a third of Germans and 23% of French respondents now consider it safe.
What's the vaccine exports row about?
The EU is concerned the UK has had an unfair advantage in contracts it signed with vaccine manufacturers, some of whom are based within the EU.
On 24 March, the European Commission said the EU had exported 10.9 million jabs to the UK since February, but that it was not aware of any vaccines going the other way.
EU leaders considered a ban on exports of vaccines to the UK but decided not to introduce one.
Instead, they called for more transparency from the UK and other countries on the number of doses they export and urged AstraZeneca to deliver what it promised.
The EU says it has exported 77 million doses to 33 countries since 1 December 2020.
What's gone wrong with the EU vaccine rollout?
In June 2020, all 27 member states joined a scheme giving the EU central responsibility for buying vaccines.
However, the EU was slower than the UK to negotiate a contract with AstraZeneca, leading to supply problems.
It also signed deals with Pfizer-BioNTech and Moderna, which saw early problems with production and distribution.
In February, European Commission President Ursula von der Leyen acknowledged the EU's vaccine failures, saying: "We were late to authorise. We were too optimistic when it came to massive production and perhaps too confident that what we ordered would actually be delivered on time."
The EU has approved the Johnson & Johnson/Janssen vaccine, and has reached agreements to buy two other vaccines - Sanofi-GSK and CureVac - once they pass clinical trials.
Can EU states make their own deals?
Member states are allowed to strike separate deals with vaccine makers which have not signed agreements with the EU.
French President Emmanuel Macron and German Chancellor Angela Merkel discussed possible co-operation with Russian President Vladimir Putin in a video conference on 30 March.
Hungary and Slovakia have already bought doses of Russia's Sputnik vaccine, and the Czech Republic is said to be considering buying it too.
Austria and Denmark have announced they are joining forces with Israel to produce second-generation vaccines against mutations of the coronavirus.
Under the terms of the EU scheme, member states are not supposed to strike deals with any vaccine manufacturer with whom the EU already has an agreement.
However, the German government signed its own side-deal with Pfizer for 30 million extra doses in September.
In January, the European Commission refused to say whether this had broken the terms of the EU scheme.
Did the UK roll out vaccines quicker because of Brexit?
The UK approved the Pfizer vaccine in November, nearly three weeks before EU regulators.
The government claimed that being outside the EU allowed it to be more nimble in this area.
However, the UK's approval of the jab would have been permitted anyway under EU law - a point made by the head of the UK medicines regulator.
The UK could have joined the EU vaccine scheme last year while it was still in a transition phase with the EU, but it chose not to.
If it had, the UK might not have been able to do as many deals with vaccine companies.