Epidemiology of VITT

Area of Science:

• Immunology
• Hematology
• Vaccinology

Background:

• Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a severe syndrome associated with adenovirus vector COVID-19 vaccines.
• VITT presents with aggressive thrombosis, thrombocytopenia, and disseminated intravascular coagulation.
• A key diagnostic feature is the presence of platelet-activating anti-PF4 antibodies post-vaccination.

Purpose of the Study:

• To summarize the characteristics and incidence of VITT.
• To highlight the distinguishing features of VITT compared to other thrombotic conditions.
• To emphasize the need for ongoing pharmacovigilance and accurate case ascertainment.

Main Methods:

• Review of reported VITT cases associated with adenovirus vector COVID-19 vaccines.
• Analysis of incidence data based on vaccine administration.
• Identification of diagnostic markers and risk factors.

Main Results:

• VITT is linked to ChAdOx1 nCoV-19 and Ad26.COV2.S vaccines.
• Incidence rates vary: 1 per 26,500-127,3000 (first dose ChAdOx1), 1 per 518,181 (second dose ChAdOx1), and 1 per 263,000 (Ad26.COV2.S).
• No clear risk factors such as sex, age, or comorbidities were identified.

Conclusions:

• VITT is a rare but critical adverse event following specific COVID-19 vaccinations.
• The presence of anti-PF4 antibodies is a distinguishing feature of VITT.
• Continued monitoring and accurate reporting are essential due to VITT's significant morbidity and mortality.