Risk of venous thromboembolism after COVID‐19 vaccination

Abstract

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.

Thrombotic events following the BNT162b2 mRNA COVID-19 vaccine (Pfizer-BioNTech) in Aotearoa New Zealand: A self-controlled case series study

“…These findings are consistent with other population based post-market studies that observed no increased risk of developing thromboembolic events following receipt of the BNT162b2 vaccine [5] , [11] , [12] , [13] , [14] , [15] . Conversely, a SCCS study in the United Kingdom (UK) found an increased risk of CVT and arterial thrombosis 15–21 days after a first dose of the BNT162b2 vaccine [6] .…”

“…New Zealand's COVID-19 Vaccine and Immunisation programme began vaccinations in February 2021 and almost exclusively uses the BNT162b2 vaccine [9] . Although the Pfizer-BioNTech phase III clinical trials [10] and subsequent international observational studies [5] , [11] , [12] , [13] , [14] , [15] have not found an association between the two, thrombotic events have been reported following the BNT162b2 vaccine through the New Zealand spontaneous reporting (passive surveillance) system [16] and internationally [17] , [18] . Moreover, a self-controlled case series (SCCS) study in England reported an increased risk of cerebral venous thrombosis (CVT) and arterial thrombosis during the 15 to 21 days after the first dose of the BNT162b2 vaccine [6] .…”

Epidemiology and prevention of venous thromboembolism

“…Immune activation through viral infections or vaccinations can lead to inflammation, and inflammation is linked to an increased risk of VTE (see sections ‘Infection’ and ‘Inflammation’). If VTE is triggered by mRNA-based vaccines, the relative and absolute risks are minuscule, because studies with millions of people who received an mRNA-based COVID-19 vaccine have not detected consistent associations with VITT 54 , 56 .…”

Venous and Arterial Thrombosis in Ambulatory and Discharged COVID-19 Patients: A Systematic Review and Meta-analysis

“…Another issue is the potential for COVID vaccines to influence the risk of VTE. In this regard, most recent studies have reported no influence of vaccines on the incidence of VTE (30,31), except perhaps for the ChAdOx1 vaccine(32) but overall it seems that vaccines are safe in this regard. This information was not available in the studies included in this review.…”