Are there any risks of thrombosis associated with vaccination against Covid-19?

Although the clinical approach against SARS-COV2 is based on a series of different therapeutic tools, vaccination is the best primary prevention against any type of infectious disease, the most effective weapon to promote herd immunity and to create a microenvironment unfavorable for virus replication and survival.

To date, the European Medicines Agency (EMA) has approved four vaccines against COVID-19: two RNA vaccines - BNT162b2 (Comirnaty® - Pfizer - BioNTech) and mRNA-1273 (Moderna) - which encode the virus spike protein antigen, encapsulated in lipid nanoparticles; ChAdOx1 nCov-19 (AstraZeneca / Vaxzevria), a chimpanzee recombined adenoviral vector encoding the SARS-CoV2 spike glycoprotein; Ad26.COV2.S (Johnson & Johnson), a recombined type 26 adenoviral vector encoding the SARS-CoV-2 spike glycoprotein.

As stated by Dr. Flora Peyvandi, Full Professor of Internal Medicine at the University of Milan and Director of the Angelo Bianchi Bonomi Hemophilia and Thrombosis Center, IRCCS Ca 'Granda Foundation Ospedale Maggiore Policlinico "There are no data demonstrating a higher incidence of thrombotic events in the vaccinated population. On the other hand, an increased risk was found for a small number of cases of complications, already very rare in themselves, which however are more frequent than expected in the population vaccinated with the AstraZeneca (Vaxzevria) and Janssen vaccines. The Pharmacovigilance Risk Assessment Commission (PRAC) of the European Medicines Agency (EMA) has concluded that there may be very rare side effects related to vaccination with these drugs". This situation has contributed and contributes considerably to generate doubts in many subjects who are increasingly moving away from the hypothesis of undergoing the vaccine peacefully, however it should be noted that all the official sources that make use of scientific and not only media support, in confirming a very rare hypothesis of vascular damage to the vaccinated subject, guarantee an efficacy far superior to the risk.

To the question: how many cases have been detected in the world so far? Professor Peyyandi continues "In the case of Vaxzevria, the AstraZeneca vaccine, the EMA evaluation involved 169 cases of cerebral venous sinus thrombosis and 53 cases of splanchnic vein thrombosis reported in the EU drug safety database (EudraVigilance) at April 4, 2021. These are cases reported spontaneously through the pharmacovigilance systems in Europe and the United Kingdom, out of a total of approximately 34 million people vaccinated. With regard to the Johnson & Johnson vaccine, the Agency evaluated 8 cases reported in the United States, out of 7 million people vaccinated (as of April 13, 2021) and in both complications assessments, the overwhelming majority of females under the age of 60 were age. There are no certainties at the moment, but a plausible explanation is that this unusual combination of blood clots and a low number of platelets results from an abnormal immune response, such as a disease AUTO IMMUNES to generate antibodies against its own platelets. It is a hypothesis born from the similarity with a condition sometimes seen in patients treated with heparin (heparin-induced thrombocytopenia, HIT), but in this case without there being any associated use of heparin, a syndrome that has been called VITT, from English vaccine-induced thrombotic thrombocytopenia".

As Vice President of the Italian Phlebological Association, I like to report the synthesis of an in-depth analysis of the scientific literature that has so far appeared in all the main journals in the world, a document that can be consulted on our official website www.associazioneflebologicaitaliana.it, analysis conducted by D. Pavei P. Director of Vascular Surgeon of the Hospital of Padua, who reminds us "...other substances besides heparin act as a trigger for a prothrombotic disorder, similar to HIT such as polyanionic drugs (for example pentosan polysulfate, the antiangiogenic factor PI-88, the hypersulfated chondroitin sulfate). Furthermore, prothrombotic syndromes have been observed after bacterial and viral infections and after orthopedic surgery. All these variants of HIT have been classified as heparin-induced autoimmune thrombocytopenia, characterized by the clinical triad of severe thrombocytopenia, disseminated intravascular coagulation and thrombosis”; therefore blaming the anti-covid vaccine as a cause of thrombosis is not only a harbinger of clinical misinterpretations, but even more seriously the cause of inappropriate "mass" doubts, responsible for false beliefs that induce European governments to adopt apparently unpopular measures.

Relatively then to the frequent questions of patients on the risk of adverse events in case of pre-existing thrombophilic disease (familial and genetic predisposition to thrombosis), this possibility is totally excluded. In fact, it must be remembered that, during the first part of the vaccination campaign, 25 million individuals were vaccinated, of which 1.5 million affected by thrombophilia, therefore with a prevalence of 6%. If we take for example the most frequent thrombophilia, i.e. the heterozygosity of factor V Leiden, with a prevalence of 5% in the world population, the absolute risk of a thrombotic event is 1 in 1000 for the population under 40, while 1 case in 100 for the population aged between 40 and 60 years. If out of 25 million vaccinated, we have had only 86 cases of VITT, then with a prevalence of 0.000003%, vaccination becomes a triggering factor for thrombosis in the genetically predisposed population with a frequency of 1 case in 100 million vaccinated patients, therefore absolutely irrelevant. And Dr. Pavei continues: "From these data we can therefore exclude the uselessness of any form of thromboprophylaxis associated with vaccination, which, on the contrary, would determine a greater risk of bleeding".

Conversely, as Dr. Corrado Lodigiani, Head of the Thrombosis and Hemorrhagic Diseases Center of Humanitas states, “what we must fear is the COVID-19 disease and not the vaccine, which is essential to protect us. If the probability of having a thrombosis after COVID-19 vaccination is about 1 in a million, 164 thousand in a million patients can develop a thrombosis in the course of COVID-19 infection. inflammation, caused by the virus above all at the level of the endothelium (the inner lining of the arteries and veins) causes an activation of the coagulation factors with consequent local thrombosis." And Lodigiani adds, concluding, "The cases observed are very rare and should not generate excessive concern: you can vaccinate and in total safety. All vaccines among those approved so far contribute significantly to preventing severe forms of COVID-19 and therefore are valuable and fundamental in dealing with the pandemic. The disease, as we have unfortunately seen over the last year, can generate very complex clinical pictures: we must not give up the vaccine out of fear, but vaccinate with confidence".

The professor Vincenzo Toschi director of the Immunohematology and Transfusion Medicine Service and Hemostasis and Thrombosis Center, ASST Santi Paolo e Carlo, Milan reminds us that the thrombosis associated with the anti-COVID-19 vaccine (VITT) has been widely disseminated by the press and represented a strong deterrent to the execution of the vaccine in large sections of the population due to the strong emotional impact it caused. However, it should be remembered that this is a very rare complication and certainly not such as to induce citizens belonging to groups not considered to be at high risk of this complication to refuse the opportunity to undergo the prophylaxis of an infection that is often very serious, in many cases fatal. , and the epidemiological trend still uncertain in the near future".

(By Paolo Casoni - from La Gazzetta di Parma of 27/10/2021 - Photo by CDC on Unsplash)