The Oxford/AstraZeneca vaccine rollout has been paused in Denmark after reports of a small number of people developing blood clots and one death.

This will understandably leave people in the UK worried if they’ve had the jab, but so far there’s no proven link between these events. The European Medicines Agency (EMA) said there’s no indication the vaccines caused these conditions.

In Vienna, a 49-year-old nurse died from severe blood coagulation problems after having the AstraZeneca vaccine and another nurse in the area, who received a dose from the same batch, developed a pulmonary embolism (a blood clot on the lung). As of March 9, there were two other reports of cases linked to clots for the same batch, according to the EMA.

As a precaution, the Health and Medicines Authority in Denmark made the decision to pause vaccination while it investigates.

Søren Brostrøm, director of the National Board of Health, said it wasn’t an easy decision to make. “But precisely because we vaccinate so many, we also need to respond with timely care when there is knowledge of possible serious side effects,” he said. 

So, what happens now?

The Danish and European pharmaceutical authorities are keeping a close eye on the roll-out of vaccines and possible side effects. In the UK, vaccination is still going ahead as normal. The EMA said the vaccine can continue while investigation of cases is ongoing, as the benefits continue to outweigh its risks. 

“It’s important to emphasise that we have not opted out of the AstraZeneca vaccine, but that we are putting it on hold,” said Brostrøm. “There is good evidence that the vaccine is both safe and effective. But both we and the Danish Medicines Agency have to react to reports of possible serious side effects, both from Denmark and other European countries.”

Professor Stephen Evans, an expert in pharmacoepidemiology from the London School of Hygiene, called Denmark’s approach “super cautious”.

In response to the news, an AstraZeneca spokesperson told the BBC: “Patient safety is the highest priority for AstraZeneca. Regulators have clear and stringent efficacy and safety standards for the approval of any new medicine, and that includes Covid-19 Vaccine AstraZeneca.” Peer-reviewed data confirmed the vaccine had been generally well-tolerated, they added.

Should you be worried?

In the UK, roughly one or two in every 1,000 people are affected by venous thrombosis (blood clots) each year. One in four people die from causes related to blood clots. People are more likely to experience them if they’ve had a prolonged stay in hospital, are overweight, smoke, use hormonal contraception, are pregnant, or have an inflammatory condition such as Crohn’s disease.

Dr Peter English, past chair of the BMA Public Health Medicine Committee, said it’s “by no means unusual” for the introduction of a vaccine to be interrupted by reports of adverse events. “This is a sign adverse reaction monitoring systems are working – but not usually a sign that the adverse reactions are caused by vaccination,” he said.

The UK is continually monitoring the safety of vaccines to ensure the benefits outweigh potential risks, added Dr Phil Bryan, vaccines safety lead for the Medicines & Healthcare products Regulatory Agency (MHRA). “It has not been confirmed that the report of a blood clot, in Denmark, was caused by the Covid-19 Vaccine AstraZeneca,” he reiterated. “The Danish authorities’ action to temporarily suspend use of the vaccine is precautionary whilst they investigate.”

More than 11 million doses of the AstraZeneca vaccine have been administered across the UK, said Dr Bryan, and reports of blood clots are “not greater than the number that would have occurred naturally in the vaccinated population”. 

Dr Bryan urged people to get their vaccine when called up for it. “The safety of the public will always come first,” he said. “We’re keeping this issue under close review but available evidence does not confirm that the vaccine is the cause.”

The number of thromboembolic events in vaccinated people is no higher than the number seen in the general population of the European Economic Area.

As of 10 March, 30 cases of thromboembolic events had been reported among close to five million people vaccinated with the AstraZeneca vaccine in the European Economic Area, which Prof Gibbins, director of the Institute for Cardiovascular and Metabolic Research at the University of Reading, pointed out “is much lower than our 1 to 2 in 1000”.

“Therefore, if there is any association between the vaccine and clotting, the risk is likely to be very low indeed,” he said. He added there’s evidence emerging that severe Covid-19 infection can cause harmful blood clots – “and so it may be the case that people are more at risk of clotting from not being immunised.” 

“We will need to see the detailed data in order to assess this properly, but at this point we also need to be careful not to cause unwarranted panic or resistance to vaccination,” he said.