A “possible link” exists between AstraZeneca’s coronavirus vaccine and rare blood clots, according to the European Union’s top drug regulator, but the benefits of the drug still outweigh its risks.
A safety committee of the European Medicines Agency (EMA) on Wednesday concluded that unusual blood clots with low blood platelets should be listed as very rare side effects of the vaccine.
Still, the agency placed no new restrictions on the use of the vaccine, which is currently being used in people age 18 and older.
The U.S. has purchased 300 million doses, the largest such deal made through the Trump administration’s Operation Warp Speed, though the shot is not yet authorized by the Food and Drug Administration.
Emer Cooke, EMA’s executive director, stressed on Wednesday that the vaccine is still a key tool in the fight against COVID-19.
“This vaccine has proven to be highly effective. It prevents severe disease and hospitalization and it is saving lives,” Cooke said during a press briefing. “We need to use the vaccines we have to protect us against the devastating effects” of the virus.
Concerns over blood clotting in a small number of recipients have dogged the shot in recent weeks, and the finding from the EMA is another blow for the vaccine, which is meant to be the backbone of a global inoculation effort.
Many European countries are relying heavily on the Oxford-AstraZeneca vaccine, as it is being sold using a nonprofit model and is far cheaper to make than other COVID-19 vaccines.
The European Union has purchased 400 million doses of the vaccine.
It is also the main shot being used by Covax, the global program to deliver vaccines to low- and middle-income countries.
Some European countries that had already authorized the vaccine have restricted its use to older populations in an effort to minimize the risk of clotting events. However, Cooke said there is no clear evidence that specific risk factors like age, gender or previous clotting history play a role.
So far, most of the cases reported have occurred in women under 60 years of age within 2 weeks of vaccination.
The blood clots occurred in veins in the brain (cerebral venous sinus thrombosis, or CVST) and a similar condition in the abdomen (splanchnic vein thrombosis) as well as in arteries. Low levels of blood platelets were sometimes reported, and occasional bleeding.
The EMA’s safety committee carried out an in-depth review of 62 cases of CVST and 24 cases of splanchnic vein thrombosis. Between the two, there were 18 fatal cases.
The cases came from the reporting systems of the European Economic Area and the United Kingdom, where 25 million people had received the vaccine.
The World Health Organization, the U.K.’s medicines regulator and the International Society on Thrombosis and Hemostasis have all said that the benefits of the vaccine outweigh the risks.
AstraZeneca has previously said its studies have found no higher risk of blood clots as a result of its vaccine.
— Updated at 11:01 a.m.
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