At a meeting held on Thursday April 7, experts from the EMA, the European Medicines Agency, concluded that these bleeding disorders should be considered as very rare side effects of the vaccine, but without explaining precisely the mechanism involved.

Abnormal reaction of the immune system

The only track mentioned is an unforeseen reaction of the immune system. Normally, they only have to fight the coronavirus. With this vaccine, there would be an abnormal response which resembles a problem already observed, very rarely, in certain types of patients: those treated with an anticoagulant, anti “clots”: heparin.

In these cases, the body begins to produce antibodies that can “activate” platelets, the main ingredients of blood clots. As if the body was fighting the anticoagulant treatment.

Unexpected role of platelets

At that time, as the platelets agglomerate to form clots, in the bloodstream, inevitably, there is less. So patients can both have blocked vessels and hemorrhages… which is difficult to treat. But beware, this exceptional reaction to heparin would never lead to the formation of clots where they are observed after vaccination with Astrazeneca, in the veins of the brain for example.

A benefit / risk ratio always favorable

Without having precisely identified the mechanism involved, the conclusion provided by the European Medicines Agency is firm: the 86 cases of atypical thrombosis occurring after 25 million injections do not call into question the protection provided by the Astrazeneca vaccine against covid. which kills thousands of people in Europe.

In other words, the famous benefit / risk ratio is affirmed as generally favorable. However, scientists have not demanded that all states of the European Union offer this vaccine to everyone.

Read also: Astrazeneca vaccine: we explain why the benefit / risk balance is favorable

Choices at the national level

On the contrary, Emer Cooke, the director of the agency, repeated that everyone had to choose their strategy according to the level of the epidemic in their country, the age of their population and the different vaccines they have …

We are here at the heart of arbitrations where pure science does not control everything. Especially since this science itself is in difficulty to establish the level of risk. In Germany, for example, the number of reported cases in relation to the number of injections is 1 per 100,000 while in the United Kingdom it is 1 in 600,000.