EMA judges AstraZeneca vaccine safe after blood clot investigation

Regulatory NewsRegulatory News | 18 March 2021 |  By 

Emer Cooke

After an all-day meeting that ran beyond its scheduled end, the safety committee of the European Medicines Agency (EMA) concluded Thursday that the benefits of receiving the AstraZeneca COVID-19 vaccine outweigh any potential risks of side effects, including thromboembolic events.
Overall, the rate of clotting events was not higher in vaccine recipients than in the general population. However, PRAC, EMA’s safety committee, is paying attention to a small subset of events that involve an unusual combination of low blood platelets and clotting.
EMA’s investigation did not turn up a batch effect, and there are no quality issues associated with any batches of AstraZeneca vaccines, clarified PRAC chair Sabine Strauss at a press conference following Tuesday’s all-day meeting.
The European countries who have paused administration of the vaccination pending the investigation must now make their own individual decisions, emphasized EMA head Emer Cooke.
“It is very important that national authorities have the right scientific basis to make their decisions,” said Cooke. “Our job is to ensure that we provide the right evidence on the vaccines so that countries can make informed decisions.” (RELATED: EMA offers reassurance on AZ vaccine, while some European authorities pause, Regulatory Focus 11 March 2021)
The recent reports, said Cooke, highlighted “that if you’re going to vaccinate a very large population of people you will always encounter certain events that occur in close temporal relationship with vaccines. We know that thromboembolic events and venous thromboembolism are very common conditions.
“These cases always occur and they will occur in temporal relationships” with vaccine administration, she said.  “If it was me, I would be vaccinated tomorrow,” but with the added context of knowing which side effects and adverse events to watch out for, added Cooke.
Asked why there should be an apparent discrepancy in rates of clotting events reported between the UK, where many more AstraZeneca doses have been administered, and EU member states, Strauss pointed out that “Populations are very different between the different member states,” and that each country has its own vaccination strategy. (RELATED: EMA, WHO investigate reported clots with AstraZeneca vaccine, Regulatory Focus 15 March 2021)
Peter Arlet, head of EMA’s data analytics and methods task force, agreed that age disparities were the most likey contributor, with the UK’s vaccines rollout primarily targeting older individuals: “The most likely explanation is the different populations being vaccinated,” he said.
EMA’s safety committee is continuing to track events that have been seen in a very small subset of AstraZeneca vaccine recipients, who have had a symptom cluster involving blood clots and thrombocytopenia with or without bleeding. Very rarely, these patients have had cerebral venous sinus thrombosis (CVST).
Eighteen CVST cases had been reported across the 20 million people in the UK and EU who have received the AstraZeneca vaccine, according to EMA. Just 7 cases of disseminated intravascular coagulation (DIC), another rare condition that involves disordered clotting and bleeding, have been reported. Though the absolute numbers are low, the rates are higher than would be expected within the vaccinated population, according to EMA.
“These are rare cases,” wrote EMA about the patients who had clotting events and low blood platelets. “A causal link with the vaccine is not proven, but is possible and deserves further analysis.”
Most of the cases involved women under the age of 50, so EMA is looking into a variety of potential contributors, including prior or undetected active COVID-19 infection, smoking, and hormonal contraception.
PRAC is continuing its review, expanding it to look at other COVID-19 vaccines, though no safety signal pointing to clotting or bleeding problems has been identified with other vaccines authorized in the EU to date. “Close safety monitoring of reports of blood clotting disorders will continue, and further studies are being instituted to provide more laboratory data as well as real-world evidence,” wrote EMA in a statement.


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