Thailand has said it will delay use of the AstraZeneca Covid-19 vaccine after several European countries temporarily suspended the jabs following reports of people suffering blood clots.
Here, we take a look at 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.
Watch: Thailand delays AZ vaccine after blood clot reports
Earlier this week, the European Medicines Agency (EMA) reported one person in Austria was diagnosed with blood clots and died 10 days after vaccination, but it stressed there is “currently no indication that vaccination has caused these conditions”.
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.
Which 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.
Some European countries have said they will not halt their AstraZeneca vaccine rollout, including Portugal, France and Germany.
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, and 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.
Are UK scientists worried?
No. 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.
They 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.”