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Summary Background Vaccination against COVID-19 is the cornerstone to control and mitigate the ongoing pandemic. Thrombotic adverse events linked to Moderna, Pfizer and the Oxford-AstraZeneca vaccine have been documented and described as extremely rare. While the Oxford-AstraZeneca vaccine has received much of the attention, the other vaccines should not go unchallenged. This study aimed to determine the frequency of reported thrombotic adverse events and clinical outcomes for these three COVID-19 vaccines, namely, Moderna, Pfizer and Oxford-AstraZeneca Methods A retrospective descriptive analysis was conducted of spontaneous reports for Moderna, Pfizer and Oxford-AstraZeneca COVID-19 vaccines submitted to the EudraVigilance database in the period from 17 February to 14 June 2021. Findings There were 729,496 adverse events for the three vaccines, of which 3,420 were thrombotic, mainly Oxford-AstraZeneca (n=1,988; 58.1%) followed by Pfizer (n=1,096; 32.0%) and Moderna (n=336; 9.8%). As serious adverse events, there were 705 reports of pulmonary embolism for the three vaccines, of which 130 reports (18.4%) were for Moderna, 226 reports (32.1%) for Pfizer and 349 (49.5%) for Oxford-AstraZeneca vaccines. The occurrence of pulmonary embolism is significantly associated with a fatal outcome (P=<0.001). Sixty-three fatalities were recorded (n=63/3420; 1.8%), of which Moderna (n=6), Pfizer (n=25) and Oxford-AstraZeneca (n=32). Interpretation Thrombotic adverse events reported for the three vaccines remains extremely rare with multiple causative factors reported elsewhere as precipitating these events. Practicing vigilance and proper clinical management for the affected vaccines, as well as continuing to report adverse events, are essential.

Competing Interest Statement

The authors have declared no competing interest.

Funding Statement

No funding was received for this study

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Paper in collection COVID-19 SARS-CoV-2 preprints from medRxiv and bioRxiv

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