One case for every 100,000 people: according to a preliminary report by the European Medicines Agency (EMA) this is the rate of venous thrombosis in atypical sites associated with thrombocytopenia in subjects vaccinated with Vaxzevria (AstraZeneca). The reports concern thrombosis of the cerebral venous sinuses and / or of the splanchnic district (abdomen), the causes of which are not yet clear even if a connection with the anti-Covid viral vector vaccines in use today is considered possible (AstraZeneca and Janssen / Johnson & Johnson).
Mutant proteins
A study ofGoethe University of Frankfurt, Germany, could help shed light on the mechanism behind rare thrombosis or even, as the headline Financial Times, to solve the puzzle of blood clots. According to the scientists, led by Rolf Marschalek, the problem would concern the viral vectors that carry the DNA fragment containing the instructions to produce the Spike (S) protein, present on the surface of the coronavirus. In the work, published online in preprint (therefore not yet reviewed by an independent expert commission), it is stated that viral vector vaccines release the Spike into the cell nucleus instead of the so-called cytosol, the intracellular fluid where the virus normally produces the protein. Once inside the cell nucleus – Marschalek and colleagues say – parts of the Spike protein divide, creating mutant versions, which are unable to bind to the cell membrane where the immune reaction takes place. The mutant proteins would be expelled from the cells and left free to circulate, triggering – in rare cases – the phenomenon of blood clots. Conversely, mRna-based vaccines (such as BioNTech / Pfizer and Moderna) release the genetic material into the cell fluid, without entering the nucleus.
The sequence of the protein S
According to the latest available data, in the UK the rare clotting reaction was recorded in 309 of the 33 million people who received the AstraZeneca vaccine, with 56 deaths. In Europe, 142 cases have been reported out of 16 million vaccine recipients. Use of the AstraZeneca vaccine has been restricted or discontinued in several countries and Janssen has added a warning on the label about the risks of rare thrombosis, although the Spike protein contained in the Janssen vaccine would be less prone to “splicing” than that of the AstraZeneca vaccine: In the United States, only 17 people out of 8 million Janssen vaccine recipients have reported the rare reaction. Marschalek and colleagues are convinced that a solution exists: developers of viral vector vaccines should, according to German scholars, modify the sequence of the Spike protein to prevent it from dividing. With the data we’ve gathered, we can tell companies how to mutate the sequences, coding the protein to prevent unwanted reactions, Marschalek pointed out.
Within three weeks
In a document drawn up by the Hemostasis and Thrombosis Working Group set up by the Italian Medicines Agency (Aifa), the experts took stock of post-vaccination thromboembolic complications with Vaxzevria and Janssen. In general, venous thromboembolic events were not more frequent than those expected in the unvaccinated population – the report reads -. However, rare cases of quite peculiar events have been ascertained, characterized by thrombosis of the cerebral venous sinuses and / or thrombosis of the splanchnic veins, often associated with the presence of thrombus in multiple sites and thrombocytopenia, with severe bleeding and sometimes signs of disseminated intravascular coagulation. These events were almost exclusively observed within approximately three weeks of vaccination in healthy subjects less than 60 years of age, mainly women.
Symptoms to observe
What are the symptoms of a thrombotic complication in the cerebral or abdominal venous system? In about 9 out of 10 cases, cerebral venous sinus thrombosis presents with headache of particular intensity. More often the pain progressively increases over a couple of days – reads the document of the Working Group on Hemostasis and Thrombosis -. Nausea and vomiting, photophobia, diplopia, decreased vision or loss of consciousness are associated. Other clinical manifestations can be seizures and neurological deficits similar to those seen after an ischemic stroke. Even in thrombosis of the abdominal veins the most common symptom is pain, often widespread and particularly intense. It can be associated with nausea and loss of appetite. Other times it occurs gastrointestinal bleeding, with the presence of blood in the stool. Thrombosis of the abdominal veins for a more subtle pathology, in which the pain reported as the first manifestation only by 6 out of 10 people and not infrequently (up to 1 out of 3 cases) diagnosed without first being clinically suspected.
May 27, 2021 (change May 27, 2021 | 14:36)
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