Thromboembolic events following mRNA vaccines for COVID 19: a case series

To the Editor, In response to the SARS-COV-2 pandemic, different types of vaccines have been developed: mRNA vaccines, non-replicative vector vaccines, inactivated and subunit vaccines [1]. By late December 2020, mass vaccination campaigns have started all around the world. Thromboembolic events have been reported after SARS-COV-2 vaccines [2], in particular after ChAdOx1 n COV-19 vaccine (Oxford- AstraZeneca) [3] and the Ad26.COV2.S (Johnson Johnson/Janssen) [4]. In these cases, a particular severe syndrome has been described (VITT) characterized by thrombosis, particularly at unusual sites including cerebral/splanchnic thrombosis, mild to severe thrombocytopenia and positive PF4-heparin ELISA and platelet activation assays [3, 5]. Despite the excellent safety profile of mRNA vaccines, some cases of venous thromboembolism(VTE) related to this type of vaccination have been recently reported in literature [6–8], including cerebral vein thrombosis [9–11]. Herein, we described our single centre experience of 15 cases of VTE following mRNA vaccination. From May 2021 to September 2021, 112 patients were admitted to our Institute for VTE. Among them, fifteen patients were admitted for the onset of a thromboembolic event occurred after the administration of mRNA vaccines. Nine were male and 6 were female. The median age was 51 years (range 29–74 years), with 13 patients younger than 60 years old. Overall, 11 patients received Comirnaty BNT 162b2 Pfizer/BioNTech vaccine while 4 the Spikevax 1273 Moderna vaccine.