“These post-vaccination thromboses are very different from common thromboses”, explains a specialist in vascular medicine.

After six cases of thrombosis, including one death in 7.5 million people vaccinated, the United States this week suspended the administration of the Jannsen vaccine for a week. After the doubts and procrastination around AstraZeneca, the cases of thrombosis, these blood clots which block a vein, post-vaccination worry.

In France, where the Jannsen vaccine is not yet available, on nearly 2.5 million injections, The Medicines Agency has listed 12 cases of these atypical thromboses, resulting in four deaths. To try to understand what is the link between these two vaccines and these thromboses, 20 minutes questioned
Marie-Antoinette Sevestre-Pietri, head of department in vascular medicine at the University Hospital of Amiens and president of the
French Society of Vascular Medicine.

Is there a greater risk of getting a thrombosis with some vaccines than others and why?

Yes, there is a greater risk of getting particular thromboses with adenovirus vaccines. That is to say that of AstraZeneca, developed with a chimpanzee adenovirus, and that of Janssen, with a human adenovirus. These vaccines induce a very strong inflammatory reaction. It activates the platelets (which make it possible to stop bleeding when you cut yourself), the number of which will drop a lot. What is called a
thrombocytopenia. The platelets that remain, they aggregate, causing a blood clot.

Is this a new or traditional reaction after a vaccine?

Create some vaccines with adenoviruses, it’s relatively new. Adenoviruses have already been used for gene therapy. You inject a modified gene to make a protein in a patient who cannot make it. We had noticed an inflammation because of these adenoviruses, but not this specific effect. We have never had a widely distributed adenovirus vaccine.

How are these thromboses specific?

What should be understood is that these post-vaccination thromboses, specific and very rare, are very different from common thromboses. First, by their location: brain and abdomen, whereas common venous thromboses are more visible on the calf, thigh and pulmonary embolism on the lungs. Another difference: they concern young people, 2/3 women. Finally, the specificity of this reaction is that it is associated with a drop in platelets and that there are chain thromboses everywhere in the body.

Which suggests an allergic reaction to heparin. Heparin is an anticoagulant [fluidifiant du sang] natural from the mucous membrane of pigs. Paradoxically, when we give this drug, we can observe an immunoallergic mechanism: the antibodies destroy the platelets. It’s rare, but it can be severe. This is also why the Danes measured the antibodies after vaccination with the same kits that are used after giving heparin.

Is this risk important to have this allergic reaction?

With Covid-19, a patient has an 8% risk of developing a venous thrombosis when he is hospitalized. In sheave, it goes up to 20%. After vaccination, 80 cases of thrombosis out of 20 million injections in the world have so far been reported. It is tiny. At the level of a population, it is very little, at the personal level, it is something else. I explain to my patients that it is necessary to be vaccinated because the risk of dying from Covid-19 is much greater than dying from these thromboses. We have seen how quickly opinion changes. At first, people were suspicious of the messenger RNA vaccine, even doctors… Today, the RNA vaccine has triumphed.

How to explain that this affects young people and women?

At the moment, we don’t know why. Maybe there are things related to hormone receptors. The over-reacting immunity in these young patients is a serious hypothesis.

What signs should alert?

After the AstraZeneca vaccine, we have seen many of our residents and medical students in our hospitals have strong inflammatory reactions. It’s normal to have fever and body aches for 24 hours. Beyond 48 hours, if it persists, however, you must be vigilant. If there are signs like a severe headache or stomach ache, blurred vision, a hand that does not work, speech problems, which are signs of stroke, you should panic.

Is there a possible preventive treatment?

Many colleagues ask us if they should give an anticoagulant for prevention. No, because this anticoagulant will have no effect on this immunological thrombosis. This medicine does not protect against this reaction. Especially since there is a risk of bleeding, so giving an anticoagulant is not a good idea.

And curative?

Yes. Since this is something new, we fumble around. But there are therapeutic possibilities. The Society of Vascular Medicine and Resuscitation have issued recommendations. Treatments depend on the platelet count. For the most serious patients, we will give an anticoagulant treatment and especially immunoglobulins to suppress these antibodies. In patients who have mild thrombocytopenia, platelets will be injected with very special anticoagulants. But there is a big mortality: a third of patients die from it, according to the available data.

How long do you have to stay vigilant? Is there a risk during the second injection?

The cases which have been described occurred between one week and 18 days after the injection. Beyond a month, this reaction is very unlikely. It is not known if there is a risk with the second injection when the first went well.

Is the risk higher for patients who already have vascular disease?

No. People who easily get thromboses, it is either a coagulation abnormality, or the circumstances, namely prolonged immobilization after surgery, during a very long plane flight… And of course, age plays a role. Thromboembolic disease is 1 in 1,000 nationally and 1 in 100 for those over 70 years old. These patients are at high risk of having severe thrombosis with Covid-19. And really very, very little risk of having an allergic reaction after the AstraZeneca vaccine. But my patients find it difficult to understand this nuance.