A point on the risk of rare thrombosis with the AstraZeneca vaccine

A study, still in pre-print, suggests that thrombotic disorders may resemble heparin-induced thrombopenia. Here's what we know so far about the link between thrombosis cases and the AstraZeneca vaccine. But let's remember: the risk / benefit balance is still clearly in favor of the vaccine

(Image: Unsplash) Accurate and in-depth analyzes have been carried out, it has been established that the benefits outweigh the risks and its leaflet has also been updated. But AstraZeneca's anti-Covid vaccine does not stop talking: in fact, the few cases of rare thrombosis following vaccination continue to worry. So much so that, after the green light from the European Medicines Agency (EMA) which has evaluated the vaccine as safe and effective, in recent days some countries have again decided to suspend it. In the Netherlands, for example, the administration has been completely blocked, while in Germany, France and Canada AstraZeneca will be administered on the basis of age, that is, those over 60 or over 55.

Only last week, EMA experts had stated that no specific risk factor, such as age, emerged from the review of the data (referring to Germany's recent stop for people under 60 years), sex or a previous medical history of bleeding disorders, for these very rare events. "A causal link with the vaccine is not proven, but it is possible and further analyzes are underway", reads the recent EMA note. Today, reports Il Messaggero, preliminary conclusions would indicate that instead there is an association with the vaccine, although it is not yet clear what the mechanism underlying these events is. This was declared by Marco Cavaleri, head of the EMA vaccine strategy, who stresses that cases are extremely rare and the benefit and risk ratio is clearly in favor of the vaccine. "But now it is increasingly difficult to say that there is no cause and effect relationship between vaccination with AstraZeneca and very rare cases of unusual blood clots associated with a low number of platelets," explains the expert. Although in-depth analyzes and assessments are still needed, this week “preliminary definitions will be provided, but we will hardly be able to indicate age limits as some countries have done”, continues Cavaleri. Based on all the data currently available, in fact, the EMA is expected to issue an updated recommendation during its April plenary meeting (April 6-9).

We also recall that a new study has suggested that the vaccine is associated with the development of thrombotic events resembling heparin-induced thrombocytopenia (Hit), which is treatable if identified early. It should be noted, however, that the research, conducted by the German drug regulatory agency Paul Ehrlich Institut and the universities of Greifswald (Germany), McMaster (Canada) and Vienna (Austria), is still in pre-print and has been published on the Research Square website, which presents studies not yet scientifically reviewed. To demonstrate the association between the vaccine and rare cases of thrombotic events, the researchers examined 9 patients in Germany and Austria, including 8 women, aged 36 years on average, who developed thrombosis following the administration, precisely between 4 and 16 days after the vaccine. Of these, 7 patients had developed cerebral venous thrombosis, one patient presented with pulmonary embolism and the last one with splanchnic venous thrombosis. Of the patients, 4 died and tested positive for antibodies to Pf4 / heparin (Pf4 means platelet factor 4) and for platelet activating antibodies. Mechanisms, the researchers explain, similar to those that occur in heparin-induced thrombocytopenia. In conclusion, the authors write, "the Azd1222 vaccine [now called Vaxzevria, ed] is associated with the development of a prothrombotic disorder that clinically resembles heparin-induced thrombocytopenia, treatable if identified early, but which exhibits a different serological profile".

The scientific director of Humanitas of Milan Alberto Mantovani also spoke about it, according to which the serious cases of thrombosis observed after the AstraZeneca vaccine "could possibly be caused, according to a recent publication, by the formation of autoantibodies , as happens, in very rare cases, during treatments with heparin: a condition called Vipt (Vaccine induced prothrombotic immune thrombocytopenia) ”, comments the expert in an interview with Corriere della sera. "If confirmed, the observation could guide the diagnosis and treatment of these, albeit very rare, adverse events".


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