Thrombosis patterns and clinical outcome of COVID-19 vaccine-induced immune thrombotic thrombocytopenia: A Systematic Review and Meta-Analysis

OBJECTIVES: To meta-analyse the clinical manifestations, diagnosis, treatment, and mortality of vaccine-induced immune thrombotic thrombocytopenia (VITT) after adenoviral vector vaccination. METHODS: Eighteen studies of VITT after ChAdOx1 nCoV-19 or Ad26.COV2.S vaccine administration were reviewed from PubMed, Scopus, Embase, and Web of Science. The meta-analysis estimated the summary effects and between-study heterogeneity regarding the incidence, manifestations, sites of thrombosis, diagnostic findings, and clinical outcomes. RESULTS: The incidence of total venous thrombosis after ChAdOx1 nCoV-19 vaccination was 28 (95% CI 12-52, I(2)=100%) per 100,000 doses administered. Of 664 patients included in the quantitative analysis (10 studies), the mean age of patients with VITT was 45.6 years (95% CI 43.8-47.4, I(2)=57%), with a female predominance (70%). Cerebral venous thrombosis (CVT), deep vein thrombosis (DVT)/pulmonary thromboembolism (PE), and splanchnic vein thrombosis occurred in 54%, 36%, and 19% of patients with VITT, respectively. The pooled incidence rate of CVT after ChAdOx1 nCoV-19 vaccination (23 per 100,000 person-years) was higher than that reported in the pre-pandemic general population (0.9 per 100,000 person-years). Intracranial haemorrhage and extracranial thrombosis accompanied 47% and 33% of all patients with CVT, respectively. The antiplatelet factor 4 antibody positivity rate was 91% (95% CI 88-94, I(2)=0%) and the overall mortality was 32% (95% CI 24-41, I(2)=69%), and no significant difference was observed between heparin- and non-heparin-based anticoagulation treatments (risk ratio 0.84, 95% CI 0.47-1.50, I(2)=0%). CONCLUSIONS: Patients with VITT after SARS-CoV-2 vaccination most frequently presented with CVT following DVT/PE and splanchnic vein thrombosis, and about one-third of patients had a fatal outcome. This meta-analysis should provide a better understanding of VITT and assist clinicians in identifying VITT early to improve outcomes and optimise management.