A number of countries suspended use of the Oxford-AstraZeneca vaccine in response to reports that some people had developed blood clots after receiving it.
Several European countries halted administration of the jab following the reports either as a precautionary measure or banned the use of a specific batch.
But the EU’s medicines regulator has said there is no indication that the Covid vaccine is linked to an increased risk of blood clots.
And the results from a US trial of the AstraZeneca vaccine were released on Monday 22 March which confirm that the jab is both highly effective and safe.
So, which countries have suspended the jab, is it linked to blood clots - and what are the common mild side effects of the vaccine?
Here is everything you need to know.
Which countries have suspended use of the AstraZeneca vaccine?
Several European countries either suspended use of the AstraZeneca jab as a precautionary measure, or banned the use of a specific batch after blood clots formed in a small number of people who had been given it.
Denmark, Norway and Iceland suspended their rollouts of the vaccine.
The EMA said Denmark’s decision was a "precautionary measure [taken] while a full investigation is ongoing into reports of blood clots in people who received the vaccine, including one case in Denmark where a person died".
No details of the Danish death have been made public, but health officials said the suspension would last for two weeks.
Norway’s public health institute said it would follow Denmark’s suspension until there was more information on any link between the vaccine and the blood clot cases.
And Iceland’s chief epidemiologist told public broadcaster Ruv to "err on the side of caution".
Meanwhile, Italy and Austria suspended different batches of the vaccine.
Italy’s medicines body called the decision “precautionary”, saying no link had been made between the jab and “serious adverse events”.
Two Italians are reported to have died after being inoculated with the AstraZeneca vaccine.
An anonymous source told Reuters news agency that the deaths were what prompted the temporary suspension.
But the Italian health authority announced on Monday 15 March that it had extended the local ban of the vaccine to become a national one.
Austria made the decision after a woman died 10 days after she was given the jab due to "severe blood coagulation problems".
Estonia, Latvia, Lithuania and Luxembourg suspended the use of the same batch as Austria, while Romania halted use of 4,200 doses from the same batch of jabs as Italy.
The Austrian doses were part of a batch of one million, identified as ABV5300, that was sent to 17 different countries in Europe.
Germany, France, Spain, Cyprus, Portugal, Slovenia and Indonesia became the latest countries to suspend the jab, announcing the move on Monday 15 March.
Sweden and Luxembourg followed suit the next day.
Some countries have started to use the jab again after Europe’s medicines regulator concluded that the vaccine is safe and effective.
Is the AstraZeneca vaccine linked to blood clots?
The US trial of the jab, run by experts at Columbia University and the University of Rochester in collaboration with AstraZeneca, found that it is safe.
More than 32,000 volunteers took part in the long-awaited study, which found there were no issues regarding blood clots.
The trial also found that the vaccine was 79 per cent effective at stopping symptomatic disease, and 100 per cent effective at preventing people from becoming seriously ill.
The EMA had previously concluded that there is no indication that the AstraZeneca jab is linked to an increased risk of blood clots.
Its review began after a report from the Norwegian Medicines Agency revealed blood clotting events in four adults who had been inoculated.
It said 30 cases of “thromboembolic events”, or blood clots, had been reported among 5 million people who had received the jab throughout Europe.
The medicines regulator made clear that the number of cases in vaccinated people was no higher than in the general population.
Executive director Emer Cooke said: “I want to also stress that at present, there is no indication that vaccination has caused these conditions (blood clots).
"They had not come up in the clinical trials, and they are not listed as known or expected side events with this vaccine.”
She said during clinical trials, vaccinated people and people who had received the placebo had shown some small numbers of blood clot developments, indicating that it is not a side effect of the jab.
She added: "The number of thromboembolic events in the vaccinated people, overall, seems not to be higher than that seen in the general population.”
A university of Oxford spokesperson echoed her statement: “Both the MHRA and EMA have said the vaccine's benefits continue to outweigh any potential risks, and the vaccine can continue to be administered while investigation of cases of thromboembolic events is ongoing, a stance also supported by the WHO.
"What we know for certain at present from real-world data is there is a clear impact of the vaccine on public health - with far fewer cases, hospitalisations, and deaths from coronavirus in those who have been vaccinated. “
The Medicines and Healthcare products Regulatory Agency (MHRA) in the UK also said there was no evidence that the jab was linked to problems.
It encouraged people to go and get their vaccination when invited to do so.
"Blood clots can occur naturally and are not uncommon. More than 11 million doses of the Covid-19 AstraZeneca vaccine have now been administered across the UK," said Phil Bryan of the MHRA.
What did the WHO say about the vaccine?
On Friday 12 March, the World Health Organisation said there was no reason not to use the AstraZeneca vaccine, stating there was no established link between the jab and blood clots.
The group’s expert advisory committee is looking at the jab following the suspension of its distribution in some European countries and will report on its findings.
Margaret Harris told a briefing that it was an "excellent vaccine" and that no causal relationship had been established between it and the health problems reported.
“It’s very important to understand that, yes, we should continue to be using the AstraZeneca vaccine,” she said.
Ms Harris added: “It is very important we are hearing safety signals because if we were not hearing about safety signals that would suggest there is not enough review and vigilance.”
What are the common AstraZeneca side effects?
The Oxford/AstraZeneca vaccine has been shown to be safe in trials, with only minor side effects observed.
This included injection-site pain, mild fever, muscle ache and headache, according to findings from the phase two safety trial which were published in The Lancet in November 2020.
The Vaccine Knowledge Group states that the most common side effect associated with this jab is fatigue, with 70 per cent of patients experiencing this.
That is closely followed by arm pain at 67 per cent, and just over half of patients experienced chills afterwards.
The least common side effect was fever at 18 per cent.
These short-term side effects are common with many vaccines - and more serious, adverse effects have not been reported.
The side effects were also less common in adults aged 56 and older, compared to younger adults.
Advice for pregnant women to avoid being vaccinated has also been amended, with those who are at risk from Covid able to receive a jab.
And people with allergies can also receive the Oxford/AstraZeneca vaccine, unless they are allergic to any of the specific ingredients.