Trends in reporting embolic and thrombotic events after COVID-19 vaccination: A retrospective, pharmacovigilance...

With the progression of global vaccination against coronavirus disease 2019 (COVID-19), embolic and thrombotic events (ETEs) following COVID-19 vaccination continue to be reported. To date, most reports on the type of COVID-19 vaccine and ETEs have been based on clinical trials, and other reports include a small number of cases. Further, the relationship between the type of COVID-19 vaccine and ETEs has not been clarified. It is important to elucidate trends in the development of ETEs after vaccination, which is a crucial concern for both prospective patients and healthcare providers. In this retrospective, pharmacovigilance study, we analyzed the Vaccine Adverse Event Reporting System (VAERS) reports from January 1, 2020 to June 18, 2021, and performed signal detection and time-to-onset analysis of adverse events by calculating the reported odds ratio (ROR) to understand ETE trends after COVID-19 vaccination based on the vaccine type. Using VAERS, we could collect data about several ETEs associated with COVID-19 vaccination. Nine adverse events associated with ETEs were reported following the administration of viral vector vaccines. The median time to ETE onset was 6 (interquartile range: 2-17) days for mRNA vaccines and 11 (interquartile range: 4-21) days for viral vector vaccines. This study suggests that VAERS aids in disequilibrium analysis to examine the association between vaccine type and ETEs after COVID-19 vaccination. Additionally, the tendency to develop ETEs and the number of days taken to develop ETEs varied depending on the type of the COVID-19 vaccine. Thus, vaccinators and healthcare providers should consider the primary diseases associated with ETEs while selecting vaccines for administration and carefully monitor patients following vaccination for potential ETEs based on the characteristics of vaccine type-specific onset period.