The European Medicines Agency said April 7 a safety committee has concluded that unusual blood clots combined with low blood platelets should be listed as a very rare side effect of AstraZeneca's COVID-19 vaccine, but that it believes the overall benefits of the vaccine in preventing COVID-19 still outweigh the risks.
As of April 4, 169 cases of cerebral venous sinus thrombosis, a type of brain blood clot, as well as 53 cases of splanchnic vein thrombosis, a blood clot in the abdomen, in people receiving AstraZeneca's vaccine have been reported to the agency, out of a total of roughly 34 million people receiving the vaccine.
Most cases have been reported in women under age 60 within two weeks of receiving the vaccine, the agency said. Specific risk factors for the blood clots haven't yet been identified.
The EMA said people who've received AstraZeneca's vaccine should seek medical assistance immediately if they develop symptoms of the combination of blood clots and low blood platelets, including shortness of breath, chest pain, leg swelling, persistent abdominal pain, neurological symptoms and tiny blood spots under the skin beyond the injection site.
A possible explanation for the blood clots is that the vaccine triggers an immune response and causes a condition similar to one seen in some patients treated with heparin, a blood thinner, the EMA said. The agency said it's conducting more studies to learn more.
The blood clots remain very rare and the benefits of the vaccine outweigh the risk of side effects, the agency said.
Britain will offer alternatives to the AstraZeneca vaccine to adults under the age of 30, The New York Times reported April 7.
Read the agency's full news release here.
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