The amazing effort of vaccination against
COVID-19, with more than 2 billion
vaccine doses administered all around the world as of 16 June 2021, has changed the history of this pandemic, drastically reducing the number of severe cases or deaths in countries were mass vaccination campaign have been carried out. However, the people's rising enthusiasm has been blunted in late February 2021 by the report of several cases of unusual thrombotic events in combination with
thrombocytopenia after vaccination with
ChAdOx1 nCov-19 (
Vaxzevria), and a few months later also after Ad26.COV2. S
vaccines. Of note, both products used an Adenovirus-based (AdV) platform to deliver the
mRNA molecule - coding for the spike
protein of SARS-CoV-2. A clinical entity characterized by cerebral and/or splanchnic vein
thrombosis, often associated with multiple
thromboses, with
thrombocytopenia and
bleeding, and sometimes
disseminated intravascular coagulation (
DIC), was soon recognized as a new syndrome, named
vaccine-induced immune thrombotic
thrombocytopenia (VITT) or
thrombosis with
thrombocytopenia syndrome (TTS). VITT was mainly observed in females under 55 years of age, between 4 and 16 days after receiving only Adenovirus-based
vaccine and displayed a seriously high fatality rate. This prompted the Medicine Regulatory Agencies of various countries to enforce the pharmacovigilance programs, and to provide some advices to restrict the use of AdV-based
vaccines to some age groups. This point-of view is aimed at providing a comprehensive review of epidemiological issues, pathogenetic hypothesis and treatment strategies of this rare but compelling syndrome, thus helping physicians to offer an up-to dated and evidence-based counseling to their often alarmed patients.