Concerning the unexpected prothrombotic state following some coronavirus disease 2019 vaccines

Abstract

Currently, the world is coping with the COVID-19 pandemic with a few vaccines. So far, the European Medicine Agency has approved four of them. However, following widespread vaccination with the recombinant adenoviral vector-based Oxford-AstraZeneca vaccine, available only in the United Kingdom and Europe, many concerns have emerged, especially the report of several cases of the otherwise rare cerebral sinus vein thrombosis and splanchnic vein thrombosis. The onset of thrombosis particularly at these unusual sites, about 5-14 days after vaccination, along with thrombocytopenia and other specific blood test abnormalities, are the main features of the vaccine side effects. The acronym vaccine-induced prothrombotic immune thrombocytopenia (VIPIT) has been coined to name this new condition, with the aim of highlighting the difference from the classic heparin-induced thrombocytopenia (HIT). VIPIT seems to primarily affect young to middle-aged women. For this reason, the vaccine administration has been stopped or limited in a few European countries. Coagulopathy induced by the Oxford-AstraZeneca vaccine (and probably by Janssen/Johnson & Johnson vaccine as well in the USA) is likely related to the use of recombinant vector DNA adenovirus, as experimentally proven in animal models. Conversely, Pfizer and Moderna vaccines use mRNA vectors. All vaccine-induced thrombotic events should be treated with a nonheparin anticoagulant. As the condition has some similarities with HIT, patients should not receive any heparin or platelet transfusion, as these treatments may potentially worsen the clinical course. Aspirin has limited rational use in this setting and is not currently recommended. Intravenous immunoglobulins may represent another potential treatment, but, most importantly, clinicians need to be aware of this new unusual postvaccination syndrome.

Cerebral Venous Sinus Thrombosis following COVID-19 Vaccination: Analysis of 552 Worldwide Cases

“…We have learned from Virchow's studies that at least three components are needed for red clot formation within the venous system [69]. Given that PF4-immune complexes are important clues for the VITT syndrome [5,8,13,55,57], other cofactors such as slow blood flow velocity and endothelial disease should also be encountered for thrombogenicity [69][70][71]. We do not know whether blood flow slowing may occur within cerebral veins in the absence of anatomical anomalies.…”

COVID-19, Vaccines, and Thrombotic Events: A Narrative Review

“…Regarding prophylaxis with antithrombotic drugs, there is no scientific evidence to support the hypothesis that aspirin or low molecular weight heparin are effective in reducing the risk of thrombotic events in subjects undergoing vaccination against COVID-19 with adenoviral vaccines, in the face of a risk of serious adverse events, such as a greater, well quantifiable, and relevant hemorrhage [184]. It is obvious that these drugs may be continued in patients already treated.…”

Alteraciones hematológicas como consecuencia de COVID-19 y sus vacunas

“…Posteriormente, este síndrome también fue reportado en individuos inmunizados con la vacuna de Johnson & Johnson [35], pero continúa en su mayoría siendo producido por la vacuna de AstraZeneca, probablemente debido a su uso más masivo [36]. Esto tuvo como consecuencia que ambas vacunas fueran suspendidas por un tiempo por las entidades reguladoras a nivel mundial [40,42,43].…”

“…Por otra parte, con las vacunas basadas en mRNA (Pfizer y Moderna), los casos reportados son pocos hasta ahora [43], y algunos autores consideran que se relacionan a condiciones preexistentes como trombocitopenia inmune y hemofilia A [36].…”

“…Como factores de riesgo asociados a VITT, se considera que son los mismos de la tríada de Virchow, sin embargo, otros factores como una infección por SARS-CoV-2 no detectada al momento de la vacunación, un estado hipercoagulable o una enfermedad autoinmune preexistente, también podrían favorecer la aparición de este síndrome, así mismo, se habla de una edad menor y del sexo femenino como factores de riesgo [36,43].…”