AstraZeneca: different leads to explain thromboses

Published by Laurent P. · Published on 6 April 2021 at 11h27 · Updated on 6 April 2021 at 12h09
As AstraZeneca vaccine seems to be indeed related to severe thrombosis cases, according to Norwegian scientists who released a study mid-March, European and French scientists are working on a lead to explain these rare cases of blood clots. Why do they occur in some people after vaccination? Keep reading to find out more.

AstraZeneca vaccine keeps on planting seeds of doubts… As the European Medicines Agency announced on Thursday March 18 the product developed by the British laboratory was “safe and effective”, after vaccinations had been halted in several European countries because of suspicious cases of thrombosis, Norwegian searchers are questioning the EMA’s decision by issuing a study led by Oslo university hospital hematology service head, stating there is a correlation between the injection of the vaccine and cases of thrombosis reported.

Furthermore, inoculation of the vaccine leads to a “powerful immune response” in some patients for whom the production of antibodies seems to interfere with platelets’ action, as Pr. Pal Andre Holme told our Norwegian peers from Verdens Gang: “There is nothing in the patient history of these individuals that can give such a powerful immune response”, he explains.

Cases of thrombosis, an injection-related mistake?

But how could the creation of blood clots be explained? Even though no formal bound has been find between the product injected and its action leading to thrombosis, French doctors and scientists from Du côté de la science group have a few early explanations. They think thromboses are not directly caused by the vaccine itself, but a poor injection. Thromboses could be cause by injecting intravenously - instead of intramuscular - leading to a "discordant immune response". Strasbourg immuno-oncology scientist Eric Billy says: "Patients with thrombosis may have had tendencies, and the intravenous injection may have led to an escalating".

Despite precautions taken to target the deltoid muscle, the injection mistake could lead to the formation of thromboses: "the presence of the adenovirus within the blood flow activaes the individula's local immune defense in an intense way to limit the spread of adenovirus", Dr. Florian Zores explains as he is also member of the group working on that matter. He goes on: "this excessive immune reaction might in some ways lead to the activation of platelets that will do what they are here for: creating blood clots".

An auto-immune reaction that cannot occur intramuscularously, unless a vein has been hit: "In the event of intravenous injection, adenovirus is found in the blood, while intracellular, it would have infected muscle cells and would not have been in the blood flow", Billy continues. He goes on: "in the blood, it is found with other cells, that rule the blood flow, the veins' permeability, all-thing blood homeostasis and therefore thrombotic ability".

How to know if the intramuscular injection worked or not? A very simple manipulation, when back from the injection, the group recommends to "check for the absence of blood flow during vaccination".

Rare blood clots past the injection

This Tuesday March 30, immunology lecturer and Head of the vaccinal strategy guidance committee Alain Fischer told our peers from France Inter about what could explain the creation of blood clots: "Several European teams - including Germans - have highlighted people who developed, five to fifteen days later, complications as thrombosis, a small decrease in platelets, and coagulation failure, what we call disseminated intravascular coagulation", he said.

He went on: "they found self-antibodies causing the platelets to stick together. This is what causes the abnormal formation of clot". He concluded: "This antibody probably is a marker of this complication, but we have left to see if there is a causal link with the vaccine".

As for the study thoroughly conducted in Norway after a young and health caretaker died ten days after being vaccinated with AstraZeneca, to brain hemorrhage, without clear link between her situation and the inoculation of the vaccine. As for the European regulator, the investigation goes on anyway. During a press brief on Thursday March 18, the EMA also stated that even though vaccinations were allowed to resume, it was required to show on leaflets given to people recently vaccinated that thromboses were likely to occur.

In France, AstraZeneca vaccination will resume this Friday March 19 including one very special vaccination: Prime Minister Jean Castex has decided to set an example and be vaccinated that day.

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