Thromboembolic events in younger women exposed to Pfizer-BioNTech or Moderna COVID-19 vaccines

Sessa, Maurizio; Kragholm, Kristian; Hviid, Anders; Andersen, Morten

Introduction: Concerns about the increased risk of blood clots associated with the VAXZEVRIA (previously named Oxford-AstraZeneca COVID-19 vaccine) and Johnson & Johnson (Janssen) COVID-19 vaccines raises the question of the thrombotic safety of other COVID-19 vaccines such as Pfizer-BioNTech or Moderna, especially in younger women, who at the early stage of the pandemic was a priority group for vaccination. Methods: Using the US-based Vaccine Adverse Event Reporting System (VAERS) and the FDA Event Reporting System (FAERS), we retrieved cases of thrombosis following vaccinations or hormonal contraceptive use in women aged ≤ 50 years. We used the reporting odds ratio (ROR) as a disproportionality measure. Results: On 19 March 2021, out of 13.6 million women aged ≤ 50 exposed to at least one dose of Pfizer-BioNTech or Moderna COVID-19 vaccines in the US, only 61 cases were reported with a total of 68 thromboembolic events (1 case per 222,951 vaccinated). None of the thromboembolic events included in our analysis were disproportionally reported for the two COVID-19 vaccines. Conclusion: Our results do support that, when compared to hormonal contraceptive use, the mRNA vaccines do not show disproportional reporting of thromboembolic events in younger women.