Perspectives on vaccine induced thrombotic thrombocytopenia

As the novel SARS-CoV-2 continues to infect numerous individuals worldwide, one of the leading approaches in dealing with the global health crisis is vaccination against the COVID-19. Due to recent reports, vaccination with ChAdOx1 nCov-19 (developed by Oxford and AstraZeneca) may result in a vaccine-induced catastrophic thrombotic thrombocytopenia disorder. Thus, as of March 16 of 2021, vaccination programs in 18 countries had been suspended until further examination, including Sweden, Germany and France. This disorder presents as extensive thrombosis in atypical sites, primarily in the cerebral venous, alongside thrombocytopenia and the production of autoantibody against platelet-factor 4 (PF4). PF4 autoantibody has the ability to binds the human FcRγIIA receptor of platelets and contribute to their aggregation. This rare adverse effect extremely resembles the clinical presentation of the classical immune-mediated HIT disorder, which occurs following exposure to heparin. Surprisingly, none of these patients had been pre-exposed to heparin before disease onset, leading to the hypothesis that a viral antigen from the vaccine had triggered the response. Importantly, COVID-19 had been associated with numerous autoimmune manifestations, including the production of pathogenic autoantibodies, new onset of autoimmune diseases and disorders. As the ChAdOx1 nCov-19 vaccination leads to the synthesis of specific SARS-CoV-2-proteins, they may trigger a production of PF4 autoantibody though molecular mimicry phenomena, while vaccination compounds lead to a rigorous bystander activation of immune cells. If existing, removing such homological sequences from the vaccine may eliminate this phenomenon. In contrast, it needs to be emphasized that the ChAdOx1 nCoV-19 vaccine was found to be safe and efficacious against symptomatic COVID-19 in randomized controlled trials, which included 23,848 participants from the UK, Brazil and South Africa.