COVID-19: Vaccine-induced immune thrombotic thrombocytopenia (VITT)

COVID-19 vaccine-induced immune thrombotic thrombocytopenia (VITT) is a rare but serious adverse event associated with the AstraZeneca viral vector COVID-19 vaccine. VITT causes blood clots accompanied by low platelets. The condition mostly occurs between 4 to 28 days after the first dose of the AstraZeneca vaccine. VITT resembles an autoimmune condition called heparin-induced thrombocytopenia (HIT). Pathologic studies show VITT is related to antibodies that activate platelets similar to HIT.
The estimated incidence of VITT is about 1 in 100,000 recipients of the first dose of the AstraZeneca COVID-19 vaccine. However, some countries have reported higher rates, up to 1 in 25,000 in Norway. The mortality rate among patients with diagnosed and treated VITT is 20 to 25 percent.
Individuals with VITT present with blood clots, most commonly in the brain, abdomen, and legs, and low platelet counts. VITT should be suspected in anyone presenting with blood clots and low platelets within 28 days of receiving the AstraZeneca COVID-19 vaccine. Treatment includes stopping heparin, administering non-heparin anticoagulants and intravenous immunoglobulin, with plasma exchange for severe cases. Prevention of the second dose is recommended in people who develop VITT after the first dose.
Awareness by clinicians of this rare syndrome and its treatment is critical as administration of heparin can worsen the condition and early treatment with non-heparin anticoagulants, immunoglobulin and plasma exchange is key to improving outcomes. Prompt reporting of suspected cases of VITT will help further understanding of this unusual complication of a viral vector COVID-19 vaccine.

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