SVM Communications: Vaccine-induced immune thrombotic thrombocytopenia (VITT)

What the vascular medicine physician should know

Leben Tefera, Scott J Cameron

What is VITT?

The pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to the rapid development of highly effective vaccines, which have proven to be the most important tool in combating the coronavirus disease 2019 (COVID-19) pandemic. Initial clinical trials reported no major adverse events beyond rare cases of anaphylaxis. As of May 19, 2021, over 1.4 billion vaccine doses have been administered.
As a result of the remarkable increase in COVID-19 vaccine administration, new reports of adverse events were reported. In particular, thrombosis in atypical vascular beds and thrombocytopenia were reported following administration of ChAdOx1 nCov-19 (AstraZeneca), a recombinant chimpanzee adenoviral vector encoding the spike glycoprotein of SARS-CoV-2, and Ad26.COV2.S (Johnson & Johnson/Janssen [JJ]), a recombinant adenovirus type 26 vector encoding the SARS-CoV-2 spike glycoprotein. This syndrome has been termed ‘vaccine-induced immune thrombotic thrombocytopenia’ (VITT). The exact incidence of VITT appears to be extremely low. Published estimates have been extrapolated from small case series and were initially estimated at one per 100,000 individuals.

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