Understanding Mechanisms of Thrombosis and Thrombocytopenia with Adenoviral SARS-CoV-2 Vaccines

Strategic Insights -

Researchers at the University of Birmingham have made significant breakthroughs in understanding thrombosis with thrombocytopenia syndrome, a rare condition linked to heparin use or COVID-19 vaccines. The study employed a comprehensive approach, analyzing data from the entire English population, and testing patient and healthy control samples for antiplatelet factor 4 antibodies. The research team identified potential mechanisms for vaccine-induced immune thrombosis and thrombocytopenia, including an electrostatic interaction between the hexon hypervariable regions of the ChAdOx1 capsid and platelet factor 4. The study also highlighted the importance of thorough reporting and real-time tracking of diseases across hospitals.

Key Takeaways:

  • The study was funded by the National Institute for Health and Care Research (NIHR) Efficacy and Mechanism Evaluation (EME) programme as award number NIHR135073.
  • The thrombosis with thrombocytopenia syndrome consortium employed a comprehensive approach across five work packages, including designing cohort studies covering the entire English population and analyzing local linked regional data sets to detect thrombosis with thrombocytopenia syndrome occurrences in real time.
  • Various patient and healthy control specimens, including those from vaccinated individuals, underwent testing for antiplatelet factor 4 antibodies using three different assays.
  • Patients who developed vaccine-induced immune thrombosis and thrombocytopenia after the AstraZeneca (AZD1222) COVID-19 vaccine underwent whole-genome and ribonucleic acid sequencing to identify genetic susceptibility factors.
  • The study revealed a higher risk of arterial and venous thromboses after COVID-19 infection compared to vaccination, with the risk of thrombosis and/or thrombocytopenia increasing after the first dose of the AZD1222 vaccine but not subsequent doses.
  • Regional linked data indicated that real-time ascertainment of diseases across multiple acute hospital sites' secure data environments is not yet feasible at scale.
  • The overall background seroprevalence of antiplatelet factor 4 antibodies was low in healthy individuals, vaccinated individuals, and those infected with COVID-19.
  • Whole-genome sequencing did not identify significant variants predisposing to vaccine-induced immune thrombosis and thrombocytopenia, with ongoing work on ribonucleic acid sequencing.
  • An electrostatic interaction between the hexon hypervariable regions of the ChAdOx1 capsid and platelet factor 4 was suggested as a possible mechanism for antiplatelet factor 4 antibody development.
  • Strong immune response drove the formation of neutrophil extracellular traps, significant inflammatory responses, and clot formation in distant organs.
  • Platelet activation post-immune complex formation against platelet factor 4 was dependent on FcgRIIa but independent of complement.
  • T-cell reactivity against the AZD1222 vaccine indicated potential cross-reactivity with prevalent human adenoviruses.

Statistics:

  • 12 (07) - Issue number of the Efficacy and Mechanism Evaluation journal article
  • NIHR135073 - Award number of the National Institute for Health and Care Research (NIHR) Efficacy and Mechanism Evaluation (EME) programme
  • 05.01.2023 - Estimated publication date of the study
  • 23 (2025) - p 145 - Page number and year of the news report

Sources:

  • "Understanding mechanisms of thrombosis and thrombocytopenia with adenoviral SARS-CoV-2 vaccines: a comprehensive synopsis." Efficacy and Mechanism Evaluation, 2025, 12(07).
  • NIHR Journals Library. https://www.journalslibrary.nihr.ac.uk/eme/
  • University of Birmingham. Department of Cardiovascular Sciences, Birmingham, United Kingdom.