Post-mortem findings in vaccine-induced thrombotic thombocytopenia

Greinacher et al.1 and Schultz et al.2 were the first to independently report the main clinical and laboratory features of 11 and five respective patients from Germany, Austria and Norway who developed life-threatening thrombohemorrhagic complications 5 to 16 days after the administration of the first dose of the chimpanzee adenoviral vector vaccine ChAdOx1nCoV-19 against SARS-CoV-2 and COVID-19. Subsequently Scully et al.3 reported similar findings in 23 patients treated with the same vaccine in the United Kingdom. More recently, See et al.4 reported a case series of 12 patients from the USA with cerebral venous sinus thrombosis following the vaccination with Ad26.CoV2.S employing a human adenoviral vector. The main post-vaccination features common to the case series were the occurrence of venous thromboembolism mainly in unusual sites (cerebral and abdominal veins) and the concomitant presence of bleeding symptoms associated with severe thrombocytopenia, often accompanied by laboratory signs of consumption coagulopathy with low plasma fibrinogen and hugely increased levels of D-dimer. The majority of reported patients reacted positively for serum immunoglobulin G (IgG) antibodies to the platelet factor 4 PF4/heparin complex. 1-4 Another common feature was the high mortality rate. The mechanism of this very rare thrombohemorrhagic syndrome was postulated to be a vaccine-triggered autoimmune reaction, with the development of antibodies against a still ill-defined PF4/polyanion complex that causes platelet activation as in heparin-induced thrombocytopenia (HIT),1-4 notwithstanding the fact that no cases were exposed to heparin before the onset of thrombosis and thrombocytopenia. We report herewith the detailed post-mortem macroscopic and microscopic findings in two similar cases that occurred in the Italian region of Sicily.