Antibody-mediated procoagulant platelets in SARS-CoV-2-vaccination associated immune thrombotic thrombocytopenia

Haematologica. 2021 Aug 1;106(8):2170-2179. doi: 10.3324/haematol.2021.279000.


The COVID-19 pandemic has resulted in significant morbidity and mortality worldwide. To prevent severe infection, mass COVID-19 vaccination campaigns with several vaccine types are currently underway. We report pathological and immunological findings in 8 patients who developed vaccine-induced immune thrombotic thrombocytopenia (VITT) after administration of SARS-CoV-2 vaccine ChAdOx1 nCoV-19. We analyzed patient material using enzyme immune assays, flow cytometry and heparin-induced platelet aggregation assay and performed autopsies on two fatal cases. Eight patients (5 female, 3 male) with a median age of 41.5 years (range, 24 to 53) were referred to us with suspected thrombotic complications 6 to 20 days after ChAdOx1 nCoV-19 vaccination. All patients had thrombocytopenia at admission. Patients had a median platelet count of 46.5 x109/L (range, 8 to 92). Three had a fatal outcome and 5 were successfully treated. Autopsies showed arterial and venous thromboses in various organs and the occlusion of glomerular capillaries by hyaline thrombi. Sera from VITT patients contain high titer antibodies against platelet factor 4 (PF4) (OD 2.59±0.64). PF4 antibodies in VITT patients induced significant increase in procoagulant markers (P-selectin and phosphatidylserine externalization) compared to healthy volunteers and healthy vaccinated volunteers. The generation of procoagulant platelets was PF4 and heparin dependent. We demonstrate the contribution of antibody-mediated platelet activation in the pathogenesis of VITT.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Autoantibodies
  • Blood Platelets
  • COVID-19 Vaccines
  • COVID-19*
  • ChAdOx1 nCoV-19
  • Female
  • Humans
  • Male
  • Middle Aged
  • Pandemics
  • SARS-CoV-2
  • Thrombocytopenia* / chemically induced
  • Vaccination / adverse effects
  • Young Adult


  • Autoantibodies
  • COVID-19 Vaccines
  • ChAdOx1 nCoV-19

Grants and funding

Funding: This work was supported by grants from the German Research Foundation and from the Herzstiftung to TB (BA5158/4 and TSG-Study), by special funds from the state of Baden-Württemberg for autopsy-based COVID-19 research and the DEFEAT PANDEMIcs network funded by the BMBF to PM and FF. JAM is supported by a grant from the German Research Foundation.