Ireland has followed several European countries who have temporarily suspended the AstraZeneca vaccine following reports of people suffering blood clots.
Here, are the key questions surrounding the situation.
What has happened?
There have been a small number of reports of people experiencing blood clots in the days and weeks after their vaccination.
Earlier this week, the European Medicines Agency (EMA) reported one person in Austria was diagnosed with blood clots and died ten days after vaccination.
However, it stressed there is "currently no indication that vaccination has caused these conditions".
The World Health Organization said this week that countries should continuing using the vaccine.
Another person was admitted to hospital in Austria with pulmonary embolism (blockage in arteries in the lungs) after being vaccinated, while one death involving a blood clot was reported in Denmark.
A 50-year-old man is also thought to have died in Italy from deep vein thrombosis (DVT), while there has been an unconfirmed report of another death in Italy.
Yesterday, Norwegian health authorities said that four people, including three health workers, who had recently received the vaccine were being treated in hospital for bleeding, blood clots and a low count of blood platelets.
What other countries are involved?
Denmark, Norway and Iceland have said they are temporarily halting all AstraZeneca vaccinations to investigate the reports.
Italy also followed Austria, Estonia, Latvia, Luxembourg and Lithuania in banning jabs from one particular batch of one million AstraZeneca vaccines, which was sent to 17 countries, after reports of a death.
Very few details have been given about the individuals, including whether they had any underlying conditions that already raised the risk of blood clots.
Thailand and Bulgaria also said this week that they would delay the roll out of the vaccine.
Some European countries have said they will not halt their AstraZeneca vaccine roll-out, including Portugal, France and Germany.
How many doses have been given in Ireland?
Of the almost 590,000 doses that have been administered here so far, Pfizer BioNTech has accounted for almost 77%, around 3% have been Moderna and AstraZeneca accounts for 20%, or 117,500 doses.
Under the EU vaccination programme, Ireland has been allocated more than 14 million doses of vaccine.
We're expecting to get 3.3 million doses of AstraZeneca which is about a quarter of our total vaccine allocation.
What do the European and UK medicines regulators say?
The UK's Medicines and Healthcare products Regulatory Agency (MHRA) has said there is no evidence to suggest the vaccine causes blood clot problems.
It said people should still get their Covid-19 jab when asked to do so.
Dr Phil Bryan, MHRA vaccines safety lead in the UK, said more than 11 million doses of the Covid-19 AstraZeneca vaccine have now been administered across the UK with no issues.
"Reports of blood clots received so far are not greater than the number that would have occurred naturally in the vaccinated population," he added.
The EMA has also backed the jab's safety, saying there are just 30 reports of blood clots among close to five million people given the vaccine across Europe.
How is the situation being treated in the UK?
The overwhelming scientific opinion is that there is no certain link between blood clots and the vaccine, and the reported cases could easily be coincidental.
Scientists in the UK argue the risks from Covid-19 far outweigh any potential side-effects from the jab, with many saying blood clots are fairly common, regardless of vaccination.
Stephen Evans, professor of pharmacoepidemiology at the London School of Hygiene & Tropical Medicine, said: "The problem with spontaneous reports of suspected adverse reactions to a vaccine are the enormous difficulty of distinguishing a causal effect from a coincidence.
"This is especially true when we know that Covid-19 disease is very strongly associated with blood clotting and there have been hundreds if not many thousands of deaths caused by blood clotting as a result of Covid-19 disease.
"The first thing to do is to be absolutely certain that the clots did not have some other cause, including Covid-19."
What has AstraZeneca said?
AstraZeneca says it has not found any increased risk of blood clots.
It said: "An analysis of our safety data of more than 10 million records has shown no evidence of an increased risk of pulmonary embolism or deep vein thrombosis in any defined age group, gender, batch or in any particular country.
"In fact, the observed number of these types of events are significantly lower in those vaccinated than what would be expected among the general population."
What happens next?
NIAC chair Professor Karina Butler told RTÉ that it will be the end of the coming week before a conclusion is reached on whether to continue administering the AstraZeneca vaccine.
Deputy CMO Dr Ronan Glynn said he hopes it will be just a one-week pause on the vaccine use as more data comes out, with the EMA investigating the risks.
Dr Glynn could not confirm if those due to have the AstraZeneca vaccine this week will be administered another vaccine or have to wait longer for the vaccine.
He also said that anyone who feels unwell more than three days after vaccination, or if they notice blue spots on their skin, they should consult a doctor immediately.
HSE Chief Clinical Officer Dr Colm Henry said those over 70 who are due to receive the Pfizer or Moderna vaccines this week will not see any disruption and the programme will continue for them as planned.
