Thrombotic Events after COVID-19 Vaccination in the Over-50s: Results from a Population-Based Study in Italy

Ileana Baldi; Danila Azzolina; Andrea Francavilla; Patrizia Bartolotta; Giulia Lorenzoni; Diego Vanuzzo; Dario Gregori

doi:10.3390/vaccines9111307

Thrombotic Events after COVID-19 Vaccination in the Over-50s: Results from a Population-Based Study in Italy

Vaccines (Basel). 2021 Nov 10;9(11):1307. doi: 10.3390/vaccines9111307.

Authors

Ileana Baldi¹, Danila Azzolina², Andrea Francavilla¹, Patrizia Bartolotta¹, Giulia Lorenzoni¹, Diego Vanuzzo³, Dario Gregori¹

Affiliations

¹ Unit of Biostatistics, Epidemiology and Public Health, Department of Cardiac Thoracic Vascular Sciences and Public Health, University of Padova, 35121 Padova, Italy.
² Department of Medical Science, University of Ferrara, 44100 Ferrara, Italy.
³ Cardiovascular Prevention Centre, 33100 Udine, Italy.

Abstract

Several European countries suspended or changed recommendations for the use of Vaxzevria (AstraZeneca) for suspected adverse effects due to atypical blood-clotting. This research aims to identify a reference point towards the number of thrombotic events expected in the Italian population over 50 years of age who received Vaxzevria from 22 January to 12 April 2021. The venous thromboembolism (VT) and immune thrombocytopenia (ITP) event rates were estimated from a population-based cohort. The overall VT rate was 1.15 (95% CI 0.93-1.42) per 1000 person-years, and the ITP rate was 2.7 (95% CI 0.7-11) per 100,000 person-years. These figures translate into 83 and two expected events of VT and ITP, respectively, in the 15 days following the first administration of Vaxzevria. The number of thrombotic events reported from the Italian Medicines Agency does not appear to have increased beyond that expected in individuals over 50 years of age.

Keywords: COVID-19; Italy; Vaxzevria; adverse events; claims data; safety.