There’s no evidence yet that AstraZeneca’s vaccine causes blood clots, and experts say any risks are outweighed by the shot’s benefits

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A vaccinator administers an injection of AstraZeneca/Oxford Covid-19 vaccine to a patient at a vaccination centre in Chester, northwest England, on February 15, 2021. Oli Scarff/AFP via Getty Images
  • Denmark and Norway suspended the use of AstraZeneca’s COVID-19 shot Thursday as a “precautionary measure”.
  • The Danish Health authorities cited concerns about blood clots in people that had received the shot.
  • Data suggests that the risk of clots is no greater than in the population at large.
  • See more stories on Insider’s business page.

Denmark, Norway, and Iceland suspended their roll out of AstraZeneca and the University of Oxford’s COVID-19 vaccine as a “precautionary” step Thursday, citing concerns about blood clots in people who had received the shot.

One person in Denmark who was immunized with the vaccine died from a blood clot, the Danish Health Authority said in a statement Thursday. At this point, it’s not known whether there is a link between the vaccine and blood clots, it said.

This follows Austrian authorities saying Sunday that a 49-year-old woman had died as a result of severe coagulation disorders after taking the shot.

The Danish Health authorities said officials “have to react” to reports of possible serious side effects, although there was “good evidence” that the vaccine was both safe and effective.

The European Medicines Agency (EMA) OK’d the shot on January 29, having looked extensively at all its safety and efficacy data, but individual countries can ultimately decide whether they give it to their citizens.

AstraZeneca vaccine and blood clots: the stats so far

There have been a total of four reported cases in Europe of people getting vaccinated with a specific batch of AstraZeneca’s shot and then developing blood clots afterwards, according to the EMA. The batch of 1 million doses had been sent to 17 EU countries, including Denmark.

At least five countries – Austria, Estonia, Lithuania, Luxembourg, and Latvia – have suspended the use of this particular batch. Norway, Denmark, and Iceland suspended the vaccine completely.

The EMA said Wednesday that one person in Europe had been diagnosed with multiple blood clots in vessels 10 days after vaccination. It was unclear whether this was the Danish case, although by that time Austrian authorities had already reported a death.

Insider contacted the Danish health authority for clarification, and a spokesperson said that they were “not at liberty to inform on the data that we receive from other authorities, national or international.”

Another person in Europe was hospitalized with a blood clot in the lung after being vaccinated, who was “now recovering,” the EMA said.

The time-frame between getting the vaccine and developing the clot for this person was not documented.

There were two other reports of blood clots, the EMA said. No further details were provided such as age, or whether they had medical conditions that made their blood more likely to clot.

No more blood clots than in general population

The EMA said in a press release that overall, as of Thursday, there had been 30 cases amongst more than 5 million who had been vaccinated with AstraZeneca’s shot overall. There was no indication that the vaccine caused blood clots, and this wasn’t a known side effect, they said.

Professor Jon Gibbons, director of the Institute of Cardiovascular and Metabolic Research at the University of Reading, said in a statement that blood clots in the general population were relatively common, and affected an average of between one and two people per 1,000 – a higher proportion than 30 in 5 million.

“Therefore if there is any association between the vaccine and clotting, the risk is likely to be very low indeed,” he said.

Dr. Phil Bryan, the Medicines and Healthcare Products Regulatory Agency (MHRA) safety lead, said in a statement that the number of reports of blood clots received so far in the UK – where more than 11 million doses of AstraZeneca’s vaccine have been given – were not greater than what would have occurred usually in a population that size.

The UK did not receive the batch from which the four most recent reports of clots arose.

Denmark’s approach ‘super’ cautious

Stephen Evans, professor of pharmacoepidemiology at the London School of Hygiene & Tropical Medicine, said in a statement that the Danish approach was “super” cautious.

“Since we know with great certainty that the vaccine prevents COVID-19, and we are almost totally uncertain that the vaccine can have caused this problem, the risk and benefit balance is still very much in favour of the vaccine in my view,” he said.

Evans said that it was difficult to distinguish between coincidence and the vaccine’s side effects.

“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.

Professor Anthony Harnden, Deputy Chair of the Joint Committee on Vaccination and Immunisation – the organization that advises the UK’s vaccine strategy – said in a statement that the public should have “confidence” that AstraZeneca’s vaccine was “safe and highly effective at preventing severe disease, including the prevention of blood clots caused by COVID-19.”