AstraZeneca vaccine: Unusual blood clots ‘very rare’ side effect of jab, EMA review finds

The AstraZeneca-Oxford vaccine appears to be linked to rare clotting disorders detected in some recipients of the jab, but remains safe to use and should continue to be administered in adults, the European Medicines Agency has said.

A review by the EMA’s safety committee concluded that “unusual blood clots with low blood platelets should be listed as very rare side effects” of the vaccine.

However, the agency said the benefits of the vaccine in providing protection against Covid-19 far outweigh its associated risk. “The risk of mortality from Covid is much greater than the risk of mortality from these side effects,” said Emer Cooke, director of the EMA.

Most of the rare blood clots reported to date have occurred in women under 60 within two weeks of vaccination — but based on the currently available evidence, the EMA said it was unable to identify specific risk factors.

Unlike the UK’s medicines regulator, which said an alternative to the AstraZeneca vaccine should be offered to 18 to 30-year-olds, the EMA has placed no new age restrictions on the jab. Nor has it recommended against administering different vaccines for younger age groups.

The reports that were investigated by the EMA centre around an extremely rare condition called cerebral venous sinus thrombosis (CVST), when blood clots in the veins that run from the brain, sometimes culminating in death.

As of 4 April, 169 cases of CVST had been reported out of 34 million doses administered across Europe.

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Clotting in the abdomen (splanchnic vein thrombosis) has also been detected, the EMA said.

In the cases of concern, these clotting disorders have been combined with thrombocytopenia, where a patient also presents abnormally low levels of platelets.

The EMA’s safety commission reviewed 62 cases of CVST and 24 cases of splanchnic vein thrombosis, which were identified among 25 million people who received the AstraZeneca vaccine. Eighteen of these were fatal, the EMA said.

Dr Sabine Straus, the regulator’s chairwoman, said the available data found a “very rare event that might occur”.

“The frequency is difficult to assess, but we feel if you state the reporting rate is approximately one in 100,000 or even a little bit higher, that would reflect the risk,” she said.

“Based on that information we ask national vaccination authorities to make up their mind on who they would like to vaccinate with which kind of vaccine.”

Safety concerns surrounding the vaccine have already prompted more than a dozen countries in recent weeks to suspend use of the jab, or restrict its use to certain groups.

Germany has limited use of the jab to people aged 60 and above, as well as high-priority individuals. This comes after the country’s medicines regulator reported 31 cases of CVST among the nearly 2.7 million people who have so far received the jab there.

Nine of the 31 people suffering clots died, and all but two of the cases involved women who were aged 20 to 63, Germany’s Paul Ehrlich Institute said. The two men were aged 36 and 57.

France approved resumed use of the vaccine on 19 March, following earlier concerns over blood clotting, but said the jab should be given to people aged 55 and over.

Spain said on 30 March it would use the vaccine for people aged 55-65, and a day later said it would extend the vaccination to essential workers aged over 65.

Canada has suspended use of the vaccine in people under 55, citing the safety data from Europe.

Dr Peter Arlett, head of data analytics at the EMA, said that oral contraceptives gave a "benchmark" of another medicine given to a healthy population that has rare side effects, pointing to the example of the contraceptive pill.

"These are given to women who are normally otherwise healthy, although obviously in a big population some of those women will have other risk factors and other conditions,” he said.

"And if we treat 10,000 women with a combined hormonal contraceptive for a year, we will see four excess blood clots in that year.”

The EMA insisted that the AstraZeneca vaccine “has proven to be highly effective, it prevents severe disease and hospitalisation and it is saving lives.”

Dr Straus added: “Vaccination is extremely important in helping us in the fight against Covid-19 and we need to use the vaccines we have to protect us from the devastating effects.”

The World Health Organisation's advisory vaccine safety panel has meanwhile said the link between the AstraZeneca vaccine and the rare cases of blood clots with low platelet counts is "considered plausible but is not confirmed".

The independent experts, in a statement issued after a review of the latest global data, said that specialised studies were needed to fully understand the potential relationship between vaccination and possible risk factors.

"It is important to note that whilst concerning, the events under assessment are very rare, with low numbers reported among the almost 200 million individuals who have received the AstraZeneca Covid-19 vaccine around the world," the panel said.

It added that it would meet against next week to review additional data.