EMA finds possible link with COVID-19 vaccine to rare and unusual blood clots

April 21, 2021

At its meeting on April 20, 2021, the European Medicines Agency’s (EMA) safety committee concluded that a warning about unusual blood clots with low blood platelets should be added to the product information for the COVID-19 vaccine from Janssen Pharmaceuticals. The committee also concluded that these events should be listed as very rare side effects of the vaccine.

However, the EMA stressed that the overall benefits of the COVID-19 vaccine from Janssen, which is part of Johnson & Johnson, outweigh the risks of side effects.

As a result of the decision, Johnson & Johnson said the company will resume shipments of the vaccine to the European Union (EU), Norway and Iceland. The COVID-19 vaccine was authorized in the EU on March 11, 2021; but the rollout of the vaccine in the EU was temporarily delayed by Johnson & Johnson after the United States paused vaccinations with the Janssen vaccine.

In reaching its conclusion, the EMA said the committee took into consideration all currently available evidence including eight reports from the United States of serious cases of unusual blood clots associated with low levels of blood platelets, one of which had a fatal outcome.

All cases occurred in people under 60 years of age within three weeks after vaccination, the majority in women. Based on the currently available evidence, specific risk factors have not been confirmed.

THE EMA’s committee noted that the blood clots occurred mostly at unusual sites such as in veins in the brain (cerebral venous sinus thrombosis, CVST) and the abdomen (splanchnic vein thrombosis) and in arteries, together with low levels of blood platelets and sometimes bleeding. The cases reviewed were very similar to the cases that occurred with the COVID-19 vaccine developed by AstraZeneca, Vaxzevria (previously COVID-19 Vaccine AstraZeneca), the EMA said.

The EMA also said one plausible explanation for the combination of blood clots and low blood platelets is an immune response, leading to a condition similar to one seen sometimes in patients treated with heparin called heparin induced thrombocytopenia, HIT.

In the United States, the Advisory Committee on Immunization Practices (ACIP) at the Centers for Disease Control and Prevention (CDC) is scheduled to meet Friday, April 23, to discuss the vaccine and the rare side effect of unusual blood clots with low blood platelets. The committee did not reach a recommendation at its meeting April 14.

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