If you want to avoid clots, get vaccinated with any vaccine available in France. “This is what tweets Professor Stéphane Gaudry, resuscitator at the Avicenne hospital in Bobigny (Seine-Saint-Denis), impressive photo of a long clot in support. He specifies that this clot, or”thrombus“, has been “removed from the leg artery of a covid patient in intensive care“.

Because if the very rare cases of thrombosis linked to the AstraZeneca vaccine and possibly to the Janssen vaccine have been making a lot of noise for several weeks, cases of thrombosis linked to covid are much less discussed. Yet their incidence is high.

Read also: Blood clots, a worrying complication of the coronavirus

One case per 100,000 vaccinated

Thus, with the data available to date, scientists estimate that the risk of declaring severe thrombosis after receiving an AstraZeneca vaccine is one case per 100,000 or 150,000 people vaccinated. And that of dying would be one for 2.5 million people vaccinated, according to theEuropean Medicines Agency.

Nearly 23% of thrombosis in intensive care

And in unvaccinated patients who have contracted the coronavirus, a risk of thrombosis also exists. A meta-analysis, covering 66 studies involving more than 28,000 patients, published in September 2020 in the scientific journal Research and Practice in Thrombosis and Haemostasis, estimated that the risk of thrombosis is 7.9% in covid patients hospitalized in the conventional sector. It rises to 22.7% in covid patients admitted to intensive care.

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Two very different thromboses

But beware, this comparison has its limits. In the case of covid patients, the virus disrupts clotting. The S protein on the surface of the coronavirus appears to bind to ACE2 receptors in blood platelets, just as it does for any target cell. This fixation would lead to platelet aggregation, which can itself lead to the formation of a clot. It is therefore a deep vein thrombosis linked to an aggregation of platelets which form a clot.

It is not at all the same phenomenon that occurs for thrombosis linked to vaccines. In this case, the most likely hypothesis is that of an immune reaction that would force the patient’s own antibodies to target their platelets. It is then a cerebral venous thrombosis, associated with an abnormality of coagulation and a fall in the number of platelets.

An “immensely favorable” benefit / risk balance

But despite these differences, the message conveyed by this tweet is clear: get vaccinated. Because the risks associated with covid are much higher than those associated with the vaccine, and without possible comparison with the benefits of vaccination.

And for the AstraZeneca vaccine, the benefit / risk balance still remains today “immensely favorable“at least for the over 55s, again recalled Professor Alain Fischer, chairman of the steering committee for the vaccination strategy, invited to C to you April 14.