COVID-19 Vaccines and Thromboembolic Events with Thrombocytopenia: Data from Italian Pharmacovigilance Public Database: An International Journal of Medical Toxicology and Drug Experience

ABSTRACT

Introduction: During large-scale vaccination campaign against COVID-19, the Italian Medicines Agency (AIFA) in collaboration with the Regional Centres of Pharmacovigilance have carried out a closely monitoring of Individual Case Safety Reports (ICSRs) about Adverse Event Following Immunisation (AEFIs) related to COVID19 vaccines and have assured a constant communication through public monthly reports1. During the first months of the vaccination campaign, a signal of rare events of thrombosis associated with thrombocytopenia2, particularly in young women, was detected by health authorities associated with the viral vector vaccines ChAdOx1S S Ad26.COV2-S. Objective: To present a comprehensive assessment of thrombotic and thromboembolic events associated with thrombocytopenia following COVID-19 immunisation with viral vector vaccines recorded in the Italian National Pharmacovigilance Network database Methods: We selected all ICSRs reported from 27 December 2020 to 26 December 2021 containing Preferred Terms (PT) related to platelet count reduction associated with PT related to thrombotic and thromboembolic events (clinical symptoms and/or diagnostic tests). All cases of thrombotic and thromboembolic events reporting thrombocytopenia in the narrative description of the report were also reviewed. The selected ICRSs were submitted to the independent evaluation of three pharmacovigilance experts who blindly classified into 5 levels of diagnostic certainty, according to the definition provided by the Brighton Collaboration Group (BCG)3. Disagreement were resolved by plenary discussion. Results: 12,166,236 doses of ChAdOx1-S and 1,500,746 of Ad26.COV2-S have been administered in Italy during the considered interval with overall 23,358/117,947 ICSRs related to ChAdOx1-S (19.8 %) and 1,580/117,947 related to Ad26.COV2-S (1.3 %). A total of 134 reports after vaccination with adenoviral vaccines were identified according to the inclusion criteria, of which 107 cases were defined as thrombotic thrombocytopenia (95 following ChAdOx1-S and 12 after Ad26.COV2-S). 27 reports were defined as "not case" (level 5, Brighton) on the basis of clinical examination or investigation, or because of the presence of heparin as a concomitant drug. Furthermore, 3 reports were excluded because of a hereditary thrombophilia or a previous history of other thrombotic episodes. Seventy-seven cases were classifiable as BCG levels 1, 2, and 3 (definite, probable and possible cases, respectively) with an overall reporting rate at about 1 case per approximately 200,000 doses administered. Women aged 30 to 49 years showed the highest reporting rates. Conclusion: In Italy, the rates of thrombotic thrombocytopenia following COVID-19 immunisation with viral vector vaccines are in line with those reported in other Countries.