Abstract
BackgroundThromboembolic and bleeding events after vaccination against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are major public concerns leading to vaccine hesitancy. Due to low incidence, an individual randomized controlled trial (RCT) is underpowered to determine whether SARS-CoV-2 vaccines increase the risks of thromboembolism and hemorrhage.MethodsWe performed a literature search using PubMed, EMBASE, Cochrane, medRxiv databases, and reference lists of relevant articles to identify RCTs that reported thromboembolic, hemorrhagic events, and thromboembolism/hemorrhage-related death after SARS-CoV-2 vaccination. The primary aim of this systematic review and meta-analysis was to estimate the pooled thromboembolic risk related to SARS-CoV-2 vaccines compared to placebo. The secondary outcomes included estimating the risks of arterial thromboembolism (ATE), venous thromboembolisms (VTE), hemorrhage, thrombocytopenia, and thromboembolism/hemorrhage-related death.ResultsEight RCTs of 4 vaccine platforms comprised of 195,196 participants were retrieved. SARS-CoV-2 vaccines were not associated with an increased risk of overall thromboembolism (risk ratio [RR], 1.14; 95% CI [confidence interval], 0.61–2.14; I2 = 35%), ATE (RR, 0.97; 95% CI, 0.46–2.06; I2 = 21%), VTE (RR, 1.47; 95% CI, 0.72–2.99; I2 = 0%), hemorrhage (RR, 0.97; 95% CI, 0.35–2.68; I2 = 0), and thromboembolism/hemorrhage-related death (RR, 0.53; 95% CI, 0.16–1.79; I2 = 0). Compared to the baseline estimated risk of these outcomes in participants administered placebos, the risk differences with vaccines were very small and not statistically significant. These findings were consistent in the subgroup analysis across 4 vaccine platforms.ConclusionVaccines against SARS-CoV-2 are not associated with an increased risk of thromboembolism, hemorrhage, and thromboembolism/hemorrhage-related death.
Highlights
Severe acute respiratory syndrome coronavirus 2 (SARSCoV-2) has been identified as a causative agent of an emerging cluster of pneumonia in China in December 2019
Due to the rarity of thrombotic and hemorrhagic events reported in individual studies, a single randomized controlled trial (RCT) is underpowered to determine whether SARS-CoV-2 vaccines increase the risks of thromboembolism and hemorrhage
The primary objective of this study was to estimate the risk of overall thromboembolism including arterial and venous thromboembolism of SARSCoV-2 vaccines compared to placebo
Summary
Severe acute respiratory syndrome coronavirus 2 (SARSCoV-2) has been identified as a causative agent of an emerging cluster of pneumonia in China in December 2019. There are at least 4 vaccine platforms including mRNA, adenoviral vector, inactivated, and protein subunit vaccines that have demonstrated effectiveness in the prevention of symptomatic infection and reduction in hospitalization and mortality from COVID-19 [3,4,5,6,7,8,9,10] These SARS-CoV-2 vaccines had acceptable safety profiles in phase 3 randomized controlled trials (RCTs), concerns regarding potential rare side effects including the risk of thromboembolism remain a reason for vaccine hesitancy [11]. An individual randomized controlled trial (RCT) is underpowered to determine whether SARS-CoV-2 vaccines increase the risks of thromboembolism and hemorrhage
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