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. 2025 Jul 30.
doi: 10.1007/s11739-025-04054-7. Online ahead of print.

Thrombotic events after vaccination for covid-19 in Italy: a report from the Italian society on thrombosis and haemostasis registry

Marco Paolo Donadini  1 , Elisa Tarasconi  2 , Lorenza Bertù  3 , Emilia Antonucci  4 , Laura Contino  5 , Valerio De Stefano  6 , Rossella Marcucci  7 , Gualtiero Palareti  4 , Laura Russo  8 , Giovanni Luca Tiscia  9 , Armando Tripodi  10 , Paolo Gresele  11 ; SISET VAX COVID-19 Working Group
Collaborators, Affiliations

Thrombotic events after vaccination for covid-19 in Italy: a report from the Italian society on thrombosis and haemostasis registry

Marco Paolo Donadini et al. Intern Emerg Med. .

Abstract

Since vaccine induced immune thrombotic thrombocytopenia (VITT) became evident in early 2021, research has focused on characterizing this new pathologic entity. Moreover, data were urgently needed on the association, if any, between all COVID-19 vaccines and thrombotic events (TEs). The study was aimed to collect relevant information on all cases of TEs occurring after COVID-19 vaccination. A national, prospective registry was set up by the Italian Society on Thrombosis and Haemostasis, enrolling consecutive adult patients diagnosed with any TE occurring within 30 days from any COVID-19 vaccine dose, with or without thrombocytopenia. The primary objective was the characterization of TEs and description of its management. The study was approved by the national ethics committee on COVID-19 research and by the participating centers. Among 308 patients included in the registry from February 2021 up to 29 Aug 2022, 276 (89.6%) were diagnosed with venous (266) and/or arterial (33) non-VITT TEs, after a median of 14 days after vaccination. The median age was 60 years, 151 (54.7%) were males, 48 (17.5%) had previous venous or arterial TEs. Within 30 days after diagnosis, 8 (2.9%) patients experienced thrombosis progression/recurrence, 2 (0.7%) major bleeding, 8 (2.9%) died. No differences were found in terms of thrombosis characteristics and progression between non-VITT patients receiving mRNA and adenoviral vector-based vaccines. The remaining 32 patients (10.4%) included in the registry were diagnosed with VITT, after a median of 10 days after vaccination. All of them received adenoviral vector-based vaccines. As compared to non-VITT thrombosis, VITT involved more often both venous and arterial sites (25% vs. 4%, p 0.0002) and unusual sites (62.5% vs. 18.8%, p < 0.0001) and was associated with worse outcomes (thrombosis progression/recurrence 25% vs. 2.9%, major bleeding 34.4% vs. 0.7%, death 18.8% vs. 2.9%, for all comparisons p < 0.0001). Significant differences were found between non-VITT and VITT cases. Non-VITT thromboses occurring after vaccination seem to resemble common thrombosis phenotypes.

Keywords: Bleeding; Thrombosis; Vaccine-induced immune thrombotic thrombocytopenia; Vaccines.

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Conflict of interest statement

Declarations. Conflict of interest: Authors have no conflict of interest to disclose. Human and animal rights statement: This study was conducted in accordance with the Declaration of Helsinki and the principles of Good Clinical Practice. Informed consent: All patients provided written informed consent prior to inclusion in the study. For retrospective cases where obtaining consent was not feasible (e.g., deceased or uncontactable patients), data were handled in compliance with European (GDPR 2016/679) and Italian privacy regulations, based on the provisions for research use without consent as permitted by national guidelines (Garante Privacy n. 9/2016, supplemented by provision n. 146/2019).

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