Cases of thrombosis are more frequent after AstraZeneca's anti-Covid vaccine than after that of Pfizer / BioNTech, even if they remain very rare, details a study published Thursday.
This therefore confirms a risk already taken into account by the health authorities.
"After a first dose (of the AstraZeneca vaccine), there is a 30% higher risk of thrombocytopenia compared to a first dose (of the Pfizer/BioNTech vaccine)," summarizes this large-scale study, published in the
British Medical Journal
( BMJ).
Thrombocytopenia is a form of thrombosis, that is, the formation of a blood clot with life-threatening consequences.
After the launch of anti-Covid vaccination campaigns in early 2021, a link was quickly suspected between viral vector vaccines (AstraZeneca and Johnson & Johnson) and the occurrence of these blood disorders.
862 cases for more than a million vaccinated
The BMJ study, carried out using health data from millions of patients across several European countries and the United States, confirms that these thromboses are more frequent after the AstraZeneca vaccine, even if their frequency remains very low: 862 cases for more than one million vaccinated.
The risk appears to be increased after the first dose.
After the second, there is no difference between the AstraZeneca and Pfizer/BioNTech vaccines.
As for the Johnson & Johnson vaccine, the data rather points in the direction of an increased risk, but not in a clear enough way for the researchers to be able to conclude frankly.
These risks must "be taken into account in future vaccination campaigns and the development of future vaccines", concludes the study.
Never approved in the USA
In fact, the AstraZeneca and Johnson & Johnson vaccines have already been largely abandoned in favor of their counterparts Pfizer/BioNTech and Moderna, both messenger RNA, in European countries.
In the United States, AstraZeneca has never been approved.
AstraZeneca and Johnson & Johnson, on the other hand, retain a central place in Covax, an international aid mechanism for Covid vaccination for less wealthy countries.
The BMJ study mainly confirms “that all vaccines [antiCovid] are safe and effective”, estimated microbiologist Sarah Pitt, who did not participate, pointing to the “extremely rare” frequency of thrombocytopenia.
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