Abstract
Two adenovirus-based vaccines, ChAdOx1 nCoV-19 and Ad26.COV2.S, and two mRNA-based vaccines, BNT162b2 and mRNA.1273, have been approved by the European Medicines Agency (EMA), and are invaluable in preventing and reducing the incidence of coronavirus disease-2019 (COVID-19). Recent reports have pointed to thrombosis with associated thrombocytopenia as an adverse effect occurring at a low frequency in some individuals after vaccination. The causes of such events may be related to SARS-CoV-2 spike protein interactions with different C-type lectin receptors, heparan sulfate proteoglycans (HSPGs) and the CD147 receptor, or to different soluble splice variants of the spike protein, adenovirus vector interactions with the CD46 receptor or platelet factor 4 antibodies. Similar findings have been reported for several viral diseases after vaccine administration. In addition, immunological mechanisms elicited by viral vectors related to cellular delivery could play a relevant role in individuals with certain genetic backgrounds. Although rare, the potential COVID-19 vaccine-induced immune thrombotic thrombocytopenia (VITT) requires immediate validation, especially in risk groups, such as the elderly, chronic smokers, and individuals with pre-existing incidences of thrombocytopenia; and if necessary, a reformulation of existing vaccines.
Highlights
The unprecedented development of several vaccines against coronavirus disease-2019 (COVID-19) promised that after 18 months of illnesses, deaths, confinements, and lockdowns, there was light at the end of the tunnel
Thrombocytopenia has been reported in 20 individuals receiving RNA-based COVID-19 vaccines, 9 vaccinated with BNT162b2 (Pfizer/BioNTech) and 11 with mRNA-1273 (Moderna) [15]
This study provides a perspective on the potential mechanisms of vaccine-induced immune thrombotic thrombocytopenia (VITT)
Summary
The unprecedented development of several vaccines against coronavirus disease-2019 (COVID-19) promised that after 18 months of illnesses, deaths, confinements, and lockdowns, there was light at the end of the tunnel. The ChAdOx1 nCoV-19 vaccine failed to provide protection against the B.1.351 variant in a clinical trial in South Africa [10]. These findings fostered the need for developing second-generation vaccines, capable of adjustment to the viral evolutionary variability and showing efficacy against newly emerged SARS-CoV-2 variants. Three cases of VITT were detected in females aged 44, 47 and 50 years at 7–12 days after the first vaccination with ChAdOx1 nCoV-19 and Ad26.COV2.S vaccines [14]. Thrombocytopenia has been reported in 20 individuals receiving RNA-based COVID-19 vaccines, 9 vaccinated with BNT162b2 (Pfizer/BioNTech) and 11 with mRNA-1273 (Moderna) [15]
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