- The Oxford-AstraZeneca shot has been dogged by safety concerns in recent weeks, with several European countries briefly suspending their use of the vaccine last month.
- 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 administering the Oxford-AstraZeneca shot far outweigh the risks.
- AstraZeneca has previously said its studies have found no higher risk of blood clots as a result of its vaccine.
LONDON — Europe's medicines regulator on Wednesday announced a possible link between the coronavirus vaccine developed by AstraZeneca and the University of Oxford and rare blood clotting issues in adults who received the shot.
It comes after a review of all currently available evidence into extremely rare cases of unusual blood clots in some vaccinated people.
Emer Cooke, executive director of the European Medicines Agency, said in a televised press conference that the regulator's safety committee "has confirmed that the benefits of the AstraZeneca vaccine in preventing Covid-19 overall outweigh the risks of side effects."
"A plausible explanation for these rare side events is an immune response to the vaccine similar to one seen in patients treated with heparin," Cooke said, noting that it's called heparin-induced thrombocytopenia.
The EMA has commissioned more research to investigate the link between the vaccine and blood clots and said its safety committee had concluded unusual blood clots with low blood platelets should be listed as "very rare" side effects of the shot. It also alerted the public to other possible side effects that will be flagged as adverse drug reactions to the vaccine's product information.
Europe's medicines regulator said it was of "great importance" that health care professionals and people receiving the Oxford-AstraZeneca vaccine were aware of these risks and look out for possible symptoms that typically occur in the first two weeks following inoculation.
"These include, for example, shortness of breath, chest pain, swelling in the leg, persistent abdominal pain, neurological symptoms including severe or persistent headache or blurred vision and skin bruising beyond the site of injection," Dr. Sabine Straus, chair of EMA's safety committee, said in the same press conference.
Shares of AstraZeneca fell nearly 1% during afternoon deals in London.
The Oxford-AstraZeneca shot has been dogged by safety concerns in recent weeks, with several European countries briefly suspending their use of the vaccine last month.
The EMA said on March 31 that it had found the shot to be safe and effective, but added it could not rule out the possibility of a causal link between the vaccine and clotting events so would continue to investigate.
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 administering the Oxford-AstraZeneca shot far outweigh the risks.
AstraZeneca has previously said its studies have found no higher risk of blood clots as a result of its vaccine.
Most countries have since resumed use of the shot but many have suspended inoculations across certain age groups.
A senior official at Europe's medicines regulator reportedly said Tuesday that there is a clear "association" between the Oxford-AstraZeneca vaccine and very rare blood clots in the brain, though the direct cause was not yet known.
In an interview with Italian newspaper Il Messaggero published Tuesday, Marco Cavaleri, chair of the EMA's vaccine evaluation team, said: "In my opinion we can now say it, it is clear that there is an association with the vaccine. However, we still do not know what causes this reaction."
The EMA subsequently denied it had established any link between the Oxford-AstraZeneca shot and rare blood clots in a statement to Agence France-Presse.
UK vaccine trial in children paused
The Medicines and Healthcare products Regulatory Agency, the body that approved the Oxford-AstraZeneca vaccine for use in the U.K., has been looking at the data following a handful of reports — both in the U.K. and in continental Europe — of serious but rare blood clots, some of which have been fatal.
A U.K. trial of the Oxford-AstraZeneca vaccine on children had already been paused while the medicines regulator investigated a possible link between the shot and the blood clotting disorders, specifically, cases of blood clots in veins within the brain, known as cerebral venous sinus thrombosis (CVST) as well as thrombocytopenia (low levels of blood platelets which help the blood to clot).
The U.K. government noted that, up to and including March 24, there had been 22 reports of CVST and 8 reports of other thrombosis events with low platelets, out of a total of 18.1 million doses of the AstraZeneca vaccine (a two-dose shot) given by that date.
"We need to know more about the people affected and we need to understand exactly how the illnesses came about, while many other questions remain unanswered at this time," Adam Finn, a professor of pediatrics at Britain's Bristol University, said ahead of Wednesday's announcement.
"However, there are some things that are very clear. The first is that these cases are very rare indeed. The second is that the vaccines that are available and in use in the UK prevent COVID very effectively," Finn said.
"In short, if you are currently being offered a dose of Oxford-AstraZeneca vaccine, your chances of remaining alive and well will go up if you take the vaccine and will go down if you don't."
— CNBC's Holly Ellyatt contributed to this report.
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