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EU, UK throw support behind AstraZeneca’s vaccine amid reports of rare blood clots

Dive Brief:

  • Drug regulators in Europe and the U.K. have reiterated their support for a coronavirus vaccine from AstraZeneca and the University of Oxford after investigating the occurrence of some abnormal blood clots soon after immunization in multiple countries.


  • Both agencies concluded the vaccine is safe and effectively prevents COVID-19. Nonetheless, the EMA wouldn’t rule out a link between the shot and rare cases of severe clots. It also recommended adding a warning label to its product information, and is launching new investigations to learn more.


  • The announcements follow decisions by several European countries to temporarily pause vaccinations with AstraZeneca’s shot, even as infections have begun to rise again across the continent. AstraZeneca has said there is “no evidence” of an increased risk of clots, citing clinical tests and real-world use.

Dive Insight:

The controversy over the safety of AstraZeneca’s vaccine in Europe has quickly escalated.

What started out as a few countries suspending vaccinations has grown to more than 20, even as it’s unclear whether the shot is causing the rare but severe clotting events now seen in 25 people in the U.K. and Europe. And that’s happened as infection rates are climbing again and some 8 million doses of AstraZeneca’s shot — one of the few available and proven to prevent COVID-19 — are reportedly unused.

A lot, then, was riding on the outcome of the investigations undertaken by U.K. and European drug regulators. They’ve been trying to determine whether the cases were incidental illnesses that just happened to occur after immunization, or side effects of the vaccine. And they had to quickly determine whether the risks of those side effects, if linked to the shot, outweighed the benefits of vaccination.

The outcome was ultimately positive for AstraZeneca. “Our scientific position is that this vaccine is a safe and effective option to protect citizens against COVID-19,” said EMA executive director Emer Cooke, in a briefing with reporters.

The EMA’s safety review committee concluded that the vaccine doesn’t increase the overall risk of blood clots, and that there are no problems with specific vaccine batches manufactured and delivered to certain countries where the incidents occurred.

What’s more, the incidents reported were rare — seven cases of clots in multiple blood vessels, and 18 cases of clots in the vessels draining blood from the brain — compared to the roughly 20 million people safely vaccinated as of March 16.

“Thousands of people in the EU die every day” from COVID-19, Cooke noted.

But the committee wouldn’t rule out a link to “very rare cases” of clots associated with very low levels of blood-clotting platelets, it said in a statement. Nine of the cases resulted in deaths, and a majority occurred in women younger than 55.

So while the EMA endorsed the shot, it will update the product information for the vaccine to include details about the risks. The agency also plans to begin an additional review and “targeted observational studies,” Cooke said.

Meanwhile, the U.K.’s Medicine and Healthcare Products Regulatory Agency issued a favorable assessment of its own. The MHRA concluded that the rare and specific clots reported can occur both naturally and as a result of COVID-19, and that a “causal association” with the vaccine hasn’t been established. A detailed review of five such cases in the U.K. is ongoing.

“We trust that, after the regulators’ careful decisions, vaccinations can once again resume across Europe,” said Ann Taylor, AstraZeneca’s chief medical officer, in a separate statement from the British drugmaker.

AstraZeneca didn’t report instances of these rare clots in clinical trials. Side effects were mostly mild to moderate, though testing was temporarily halted when a participant developed a neurological illness that regulators couldn’t link to vaccination.

Results from AstraZeneca’s largest study, a Phase 3 trial of more than 32,000 volunteers in the U.S. and South America, are expected imminently.