France has already received 200,000 doses, and hoped to receive two more million by the end of April. But the future of Johnson & Johnson’s Janssen vaccine could be called into question by a new alert. The American health authorities have in fact suspended its use in the United States following the appearance of six cases of atypical thrombosis, including one death, out of 6.8 million vaccinated. Symptoms appeared between 6 and 13 days after the injection.

Are adenoviruses involved?

These cases are reminiscent of those which have mobilized the European Medicines Agency in recent weeks around the AstraZeneca vaccine. These two vaccines use adenovirus technology, unlike the Pfizer and Moderna vaccines which use messenger RNA technology. The viral support could explain this difference in risk of thrombosis between these two vaccine technologies, but this is only a hypothesis that will of course have to be verified.

Do not use heparin treatment

Why have health authorities chosen to pause vaccinations? “We are taking this break so that in the face of these symptoms, in the event of a clot diagnosis, every doctor now thinks of asking the question of the vaccine”. This is their message. Because the stake is major: one must not then use heparin, the most common of the anticoagulant treatments, “anti-clot”. This is what recent German and Swedish studies have taught us, because this treatment could on the contrary worsen the situation in these very specific thromboses associated with a shortage of platelets.

An American committee of experts is meeting today. They need to find out if there really is a link between the Janssen vaccine and these abnormalities, which remain extremely rare.

If France has announced that the 200,000 doses already received of Janssen vaccine will be administered as planned, the European Medicines Agency must issue a new opinion next week on this vaccine.