Risk of venous thromboembolism after COVID-19 vaccination

Background: COVID-19 vaccinations in the United States are effective in preventing illness and hospitalization yet concern over post-vaccination venous thromboembolism (VTE) risk has led to vaccine hesitancy. Methods: The aim of this study was to compare VTE rates before and after COVID-19 vaccination. COVID-19 vaccinated patients ≥18 years between November 1, 2020 through November 1, 2021 were analyzed using electronic medical records across the Mayo Clinic enterprise. The primary outcome was imaging confirmed acute VTE (upper or lower deep vein thrombosis or pulmonary embolism) occurring 90 days before and after the date of first vaccine dose. Results: A total of 792 010 patients with at least one COVID-19 vaccination were identified (Pfizer, n = 452 950, Moderna, n = 290 607, and Janssen [Johnson & Johnson], n = 48 453). A total of 1565 VTE events occurred in the 90 days before (n = 772) and after (n = 793) COVID-19 vaccination. VTE post-vaccination occurred in 326 patients receiving Moderna (0.11%, incidence rate [IR] 4.58 per 1000p-years), 425 patients receiving Pfizer (0.09%, IR 3.84 per 1000p-years), and 42 receiving Janssen (0.09%, IR 3.56 per 1000p-years). Compared to the pre-vaccination timeframe, the adjusted hazard ratio (aHR) for VTE after the Janssen vaccination was 0.97 (95% confidence interval [CI] 0.63–1.50), aHR 1.02 (95% CI 0.87–1.19) for Moderna, and aHR 1.00 (95% CI 0.87–1.15) for Pfizer. Conclusion: In this large cohort of COVID-19 vaccinated patients, no increased risk for acute VTE post-vaccination was identified for the authorized vaccines in the United States.