Laboratory confirmed vaccine-induced immune thrombotic thrombocytopenia: Retrospective analysis of reported cases after vaccination with ChAdOx-1 nCoV-19 in Germany

BACKGROUND: Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a severe adverse event of SARS-CoV-2 vaccination. We describe the characteristics of patients reported in Germany based on the Brighton Collaboration (BC) case definition criteria for Thrombosis and Thrombocytopenia Syndrome (TTS) and focus on patients with complete anti-platelet factor 4 (PF4)-antibody laboratory work up. METHODS: The adverse drug reaction database of the Paul-Ehrlich Institute was queried for TTS cases following ChAdOx1 nCoV-19 vaccination from February 1, until May 21, 2021. Cases with reports from the Greifswald laboratory were analysed in detail. FINDINGS: PF4 antibody tests were available for 69 suspected TTS cases reported to the Paul-Ehrlich Institute, of whom 52 patients fulfilled the BC case definition; 37 (71%) women, 15 (29%) men, median age 46·0 years (interquartile range 31·0-60·3 years). Cerebral venous sinus thrombosis was confirmed in 37 (71%), (additional) multiple thromboses in 19 (37%) patients. Twelve patients died. Non-survivors showed lower platelet counts compared to survivors (median nadir 15,000/µL vs 49,000/µL; p<0·0001). Combined anti-PF4/heparin IgG ELISA and PF4-dependent platelet activation testing yielded sensitivity of 96% (95% confidence interval 87-100%) and specificity of 77% (50-93%) for TTS. Four patients with thrombocytopenia but without thrombosis presented with severe headache or cerebral bleeding, explaining the lower specificity. INTERPRETATION: VITT has high mortality and can present with isolated thrombocytopenia, severe headache, and bleeding. Demonstration of platelet activating anti-PF4 IgG has high sensitivity for TTS and captures a wider spectrum of clinically relevant VITT than the current BC case definition