The European Medicines Agency has now launched an investigation while the vaccine continues to be used without interruption in the UK. Denmark, Norway and Iceland have all suspended use of the vaccine, while Austria and Italy have stopped the use of a particular batch.
The Danish health authority said rollout of the jab will be paused for 14 days while an investigation is carried out.
Danish health minister Magnus Heunicke said on Twitter: “It is currently not possible to conclude whether there is a link. We are acting early, it needs to be thoroughly investigated.”
The number of people suffering from blood clots since receiving the vaccine has not been disclosed.
Austrian authorities have confirmed two people developed blood clots following administration of the jab.
Italy’s medical regulator AIFA said: “Following the reporting of some serious adverse events… AIFA has decided, as a precaution, to issue a ban on the use of this batch throughout the national territory.”
Does the Oxford vaccine cause blood clots?
No research has been completed to establish a link between the Oxford vaccine and blood clots, but UK regulators and experts have defended the vaccine, insisting it is safe for use.
Dr Phil Bryan, MHRA vaccines safety lead in the UK, said: “The Danish, Norwegian and Icelandic authorities’ action to temporarily suspend use of the vaccine is precautionary whilst they investigate. 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.
“Reports of blood clots received so far are not greater than the number that would have occurred naturally in the vaccinated population.”
Professor Anthony Harnden, deputy chairman of the Joint Committee on Vaccination and Immunisation, said: “Vaccine safety is critically important.
“Our UK regulator, the MHRA, review all reports of adverse events for both vaccines as they are reported.
“The public should have confidence that both vaccines used in the UK vaccination programme are safe and highly effective at preventing severe disease, including the prevention of blood clots caused by Covid.”
Professor Stephen Evans from the London School of Hygiene & Tropical Medicine said: “This is a super-cautious approach based on some isolated reports in Europe.
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“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.”
He said it was a “sensible approach” to investigate, but added: “The risk and benefit balance is still very much in favour of the vaccine in my view.”
In a statement, AstraZeneca said patient safety was its “highest priority” and regulators have “clear and stringent efficacy and safety standards” for the approval of new medicines and vaccines.
It said: “The safety of the vaccine has been extensively studied in phase three clinical trials and peer-reviewed data confirms the vaccine has been generally well-tolerated.”
A blood clot is a clump of blood that has changed from its usual liquid state into a semisolid state.
Clotting is a normal process that can stop you from losing blood if you injure yourself, but if a clot forms inside you it won’t always dissolve on its own.
Immobile blood clots are usually harmless, but if it moves it can travel through your veins and prevent blood flow, which is a medical emergency.