No change of course for adenovirus vaccines. In an opinion made public on Wednesday 12 May, the National Agency for Medicines and Health Products Safety (ANSM) confirmed the position taken so far by the French health authorities: the vaccines of AstraZeneca and Johnson & Johnson must continue to be delivered to “Older populations” in whom the benefit / risk ratio is “Particularly marked”. Vaccination for over 55s “Can be maintained”, indicates the agency. On the other hand, “Experts have reservations about the use of adenoviral vector vaccines in the youngest in view of the risk of complications linked to thrombosis with thrombocytopenia and the more limited expected individual benefit”.
This position was adopted by the ANSM following three meetings held by a “temporary scientific committee” (CST) made up of members of the agency and around fifteen outside specialists, researchers, clinicians and user associations. . Faced with accidents occurring in subjects who had been vaccinated with the product from the Anglo-Swedish laboratory, this committee set itself the task of both shedding light on the mechanisms at the origin of these atypical thromboses and identifying the risk factors and possible preventive measures, and finally to examine the expected benefit / risk ratios in order to draw recommendations. Thirty cases of atypical thrombosis have been counted in France, including nine deaths.
Experts confirm that the mechanism “Most likely” of these thromboses, localized in the brain and the abdomen, and presenting a high mortality, between 20 and 30%, “Is an autoimmune reaction linked to the presence of antibodies directed against a protein in platelets”. The precise origin of this reaction, which occurs between the 4e and the 28e day after vaccination, “Is still unknown”, indicates the ANSM. But the experts clearly favor a suspect: the adenovirus. “If the problem came from the Spike protein which serves as an antigen, we should have observed these atypical thromboses with messenger RNA vaccines, this is not the case, indicates the pharmacologist Pierre Démolis, scientific advisor to the ANSM and president of the CST. They only appeared in Europe after the use of the AstraZeneca vaccine and in the United States with that of Johnson & Johnson. However, both use an adenoviral vector. “
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