Letter to the Editor
"All COVID-19 vaccines use the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein as the antigenic substrate. However, serious adverse reactions have been reported, including more than 150 cases of thrombocytopenia after vaccination. A precise mechanism linking COVID-19 vaccination and severe thrombocytopenia has yet to be confirmed.
The serotonin release assay (SRA) is the gold standard diagnostic test for heparin-induced thrombocytopenia (HIT), which is characterized by severe thrombocytopenia and a risk of thrombosis. By using the SRA, we recently showed that a subset of critically ill patients with COVID-19 tested positive for platelet-activating immune complexes. Similarly, Althaus showed that immunoglobulin G (IgG) antibodies from critically ill patients who have COVID-19 can also activate platelets and lead to thrombotic events. Here, we used a modified SRA to demonstrate spike-dependent, platelet-activating immune complexes in a patient who had vaccine-induced thrombocytopenia (VIT) after receiving the Moderna COVID-19 mRNA vaccine...
It is important to recognize that the mechanism described here is different from the recently reported, extremely rare HIT-like [heparin-induced thrombocytopenia] syndrome known as vaccine induced thrombotic thrombocytopenia (VITT). In VITT, patients present with life-threatening thrombosis in the context of strongly positive, platelet activating anti-PF4/heparin antibodies that present following adenoviral-based COVID-19 vaccination. The mechanism of VIT proposed here is independent of anti-PF4/heparin antibodies seen in VITT and presents differently....
Ultimately, the role of SARS-CoV-2 spike protein requires further clarification in regard to platelet activation and its role in vaccine- and PEG-dependent platelet activation. We postulate that the small subset of antibodies against the spike protein that formed after vaccination can activate platelets and cause thrombocytopenia. The prevalence of this phenomenon still needs to be clinically determined. Regardless, the modified SRA presented here may be a useful diagnostic test as more cases of VIT are recognized."
© 2022 by The American Society of Hematology.
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