Comparison of adverse drug reactions among four COVID-19 vaccines in Europe using the EudraVigilance database: Thrombosis at unusual sites

Background: Real-world experience with adenoviral vector vaccines against COVID-19 raised some safety concerns. Cases of cerebral vein thrombosis (CVT) associated with thrombocytopenia have been observed after the first dose of the adenoviral vector vaccines CHADOX1 NCOV-19 and AD26.COV2.S.

Objectives: To assess the reporting rate of CVT as adverse drug reaction (ADR) for the COVID-19 vaccines authorized in Europe.

Patients and methods: This observational study assessed the CVT reporting rate attributed to four COVID-19 vaccines authorized in Europe, namely Tozinameran (Pfizer-Biontech), CX-024414 (Moderna), CHADOX1 NCOV-19 (AstraZeneca), and AD26.COV2.S (Janssen). Data on thrombotic ADRs reported on EudraVigilance database between January 1, 2021 and July 30, 2021, were collected. ADRs referring to CVT were identified. The reporting rate of CVT was expressed as 1 million individual vaccinated-days with 95% confidence interval. Finally, an observed-to-expected (OE) analysis was performed.

Results: The reporting rate of CVT per 1 million person vaccinated-days was 1.92 (95% confidence interval [CI], 1.71-2.12) for Tozinameran, 5.63 (95% CI, 4.74-6.64) for CX-024414, 21.60 (95% CI, 20.16-23.11) for CHADOX1 NCOV-19, and 11.48 (95% CI, 9.57-13.67) for AD26.COV2.S. CVT occurred alongside thrombocytopenia for the four vaccines. The OE ratio was greater than one for all four vaccines, both with the lowest and the highest CVT background incidence.

Conclusions: This report on EudraVigilance data strengthens anecdotal findings on CVT following COVID-19 vaccinations. Although the European Medicines Agency released an alert only for CHADOX1 NCOV-19 and AD26.COV2.S, Tozinameran and CX-024414 also are complicated by CVT, albeit to lesser extent.