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Regulatory Focus™ > News Articles > 2021 > 4 > "Very rare" thrombotic events with AZ vaccine, concludes EMA's PRAC

"Very rare" thrombotic events with AZ vaccine, concludes EMA's PRAC

Posted 09 April 2021 | By Kari Oakes 

AstraZeneca’s COVID-19 vaccine may have a “very rare” but serious side effect of unusual blood clotting with a low blood platelet account, concluded the safety committee of the European Medicines Agency (EMA). The benefits of receiving the vaccine still outweigh risks, said the committee, hewing to the line EMA has held to throughout the investigation into reports of clotting events with the AstraZeneca vaccine.
 
The conclusion reached by EMA’s Pharmacovigilance Risk Assessment Committee (PRAC) came from its April meeting where “the committee took into consideration all currently available evidence, including the advice from an ad hoc expert group.” (RELATED: AstraZeneca vaccine deemed safe by EMA, again, Regulatory Focus 31 March 2021)
 
Most of the cases reported by healthcare professionals have been in women younger than 60 and have occurred within two weeks of receipt of the AstraZeneca vaccine, now known as Vaxzevria. In these rare occurrences, patients had splanchnic vein or cerebral venous sinus thromboses, or arterial clots, together with thrombocytopenia and sometimes bleeding events.
 
PRAC’s in-depth review included 62 cerebral venous sinus thrombosis cases and 24 occurrences of splanchnic vein thrombosis that ad been reported into EudraVigilance by 22 March 2021. Eighteen of these patients died. The 86 cases were reported primarily from within the European Economic Area and the UK, where about 25 million people have thus far received Vaxzevria.
 
PRAC’s investigation will now turn to uncovering a potential proximate cause for these events; “[o]ne 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 (heparin induced thrombocytopenia, HIT),” wrote EMA in announcing PRAC’s conclusions. The committee “has requested new studies and amendments to ongoing ones.”
 
Friday, PRAC also announced that it is beginning an investigation into a safety signal related to reports of capillary leak syndrome. Five cases of this rare disorder, which involves“third-spacing” of fluid from blood vessels with a resulting drop in blood pressure, have been reported into EudraVigilance.
 
At this stage, it is not yet clear whether there is a causal association between vaccination and the reports of capillary leak syndrome. If PRAC’s investigation confirms a causal relationship, EMA will take such appropriate regulatory action as updating its summary of product characteristics and the package leaflet.
 
Looking at another COVID-19 vaccine, PRAC has also started to investigate four reports of unusual blood clots with thrombocytopenia after receipt of the vaccine developed by Janssen, the vaccines subdivision of Johnson & Johnson. Of the four patients affected, one was participating in a clinical trial and three received the vaccines during the US rollout. One of the patients died, reported PRAC.
 
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Tags: coronavirus, EMA, PRAC

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