SARS-CoV-2 vaccine-induced immune thrombotic thrombocytopenia: A comprehensive review, release 1 (epidemiologic perspective)

More than eight billion vaccine doses have been delivered to battle the COVID-19 pandemic. SARS-CoV-2 vaccines have been carefully developed and proven efficacious as evidenced by clinical assays and studies in real-world settings. However, rare but severe side effects raise important safety concerns. Particularly, severe complication after vaccination with adenoviral vector vaccines, vaccine-induced immune thrombotic thrombocytopenia (VITT), has attracted worldwide attention. It is characterized by thrombosis at unusual sites, including cerebral or abdominal thrombosis, thrombocytopenia, and the presence of antibodies against platelet factor 4. Although rare, VITT progresses rapidly with a high mortality rate, and new severe symptoms continue to appear with increased VITT vigilance, and a growing body of evidence. The COVID-19 pandemic is still ongoing with continuously emerging variants. It is therefore important to vaccinate a large population and work to overcome current vaccine limitations. The scientific community needs to be aware of specific side effects and understand their exact mechanisms in order to overcome vaccine hesitation.