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Updated: Aug 12, 2025
Microfluidics in Assessing Platelet Function
Published on: November 8, 2024
Head-to-head comparison of four COVID-19 vaccines on platelet activation, coagulation and inflammation. The TREASURE
Marta Brambilla1, Paola Canzano1, Patrizia Della Valle2
1Centro Cardiologico Monzino IRCCS, Milan, Italy.
Insights
COVID-19 vaccines did not cause platelet activation but induced a transient inflammatory response. Minor changes in clotting and endothelial function may explain rare vaccine-related thromboembolic events.
Area of Science:
- Immunology and Vaccinology
- Hematology and Thrombosis
- Infectious Diseases and Public Health
Background:
- Conflicting studies exist on COVID-19 vaccine effects on blood coagulation and platelet activation.
- Assessing vaccine-induced changes in coagulation, platelet function, and inflammation is crucial.
Purpose of the Study:
- To evaluate the impact of four COVID-19 vaccines (viral vector and mRNA) on platelet activation, coagulation, and inflammation.
- To investigate the influence of immunization dose and prior SARS-CoV-2 infection history.
Main Methods:
- The TREASURE study analyzed 368 participants receiving viral vector or mRNA COVID-19 vaccines.
- Flow cytometry assessed platelet activation markers and microvesicles.
- Calibrated Automated Thrombogram measured thrombin generation; ELISA analyzed coagulation and inflammation markers.
Main Results:
- No significant platelet activation or microvesicle release was observed post-vaccination.
- Transient increases in IL-6, CRP, D-dimer, and fibrinogen were noted across all vaccines.
- Minor reductions in aPC, TM, and TFPI were observed, suggesting potential endothelial effects; no anti-PF4 antibodies were detected.
Conclusions:
- COVID-19 vaccines induce a transient inflammatory response without initiating platelet activation.
- Minor alterations in clotting and endothelial function may contribute to understanding rare thromboembolic complications.
- Findings suggest a favorable safety profile regarding thrombotic events for the studied COVID-19 vaccines.
Introduction:
Studies exploring alterations in blood coagulation and platelet activation induced by COVID-19 vaccines are not concordant. We aimed to assess the impact of four COVID-19 vaccines on platelet activation, coagulation, and inflammation considering also the immunization dose and the history of SARS-CoV-2 infection.
Methods:
TREASURE study enrolled 368 consecutive subjects (161 receiving viral vector vaccines -ChAdOx1-S/Vaxzevria or Janssen- and 207 receiving mRNA vaccines -Comirnaty/Pfizer-BioNTech or Spikevax/Moderna). Blood was collected the day before and 8 ± 2 days after the vaccination. Platelet activation markers (P-selectin, aGPIIbIIIa and Tissue Factor expression; number of platelet-monocyte and -granulocyte aggregates) and microvesicle release were analyzed by flow cytometry. Platelet thrombin generation (TG) capacity was measured using the Calibrated Automated Thrombogram. Plasma coagulation and inflammation markers and immune response were evaluated by ELISA.
Results:
Vaccination did not induce platelet activation and microvesicle release. IL-6 and CRP levels (+30%), D-dimer, fibrinogen and F1+2 (+13%, +3.7%, +4.3%, respectively) but not TAT levels significantly increased upon immunization with all four vaccines, with no difference among them and between first and second dose. An overall minor post-vaccination reduction of aPC, TM and TFPI, all possibly related to endothelial function, was observed. No anti-PF4 seroconversion was observed.
Conclusion:
This study showed that the four COVID-19 vaccines administered to a large population sample induce a transient inflammatory response, with no onset of platelet activation. The minor changes in clotting activation and endothelial function might be potentially involved at a population level in explaining the very rare venous thromboembolic complications of COVID-19 vaccination.
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