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What is vaccine-induced thrombosis and thrombocytopenia (VITT)?

This article was published on
April 16, 2021

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Professor Beng Chong an expert on heparin-induced thrombocytopenia (HIT), a condition that closely resembles the blood clot condition linked to the AstraZeneca vaccine. Professor Chong explains what we know about vaccine-induced thrombosis and thrombocytopenia.

Professor Beng Chong an expert on heparin-induced thrombocytopenia (HIT), a condition that closely resembles the blood clot condition linked to the AstraZeneca vaccine. Professor Chong explains what we know about vaccine-induced thrombosis and thrombocytopenia.

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What is vaccine-induced thrombosis and thrombocytopenia (VITT) (also known as ‘vaccine induced prothrombotic immune thrombocytopenia’ (VIPIT))?

VITT is almost like heparin-induced thrombocytopenia (HIT). HIT is a severe immune reaction triggered by a drug (heparin). VITT is triggered by a COVID19-vaccine. The symptoms, reduction in platelets (blood cells that form clots), severe clot formation at rare sites, the disease-causing antibody, lab tests, and treatment are almost the same in HIT and VITT.

What is the difference between Vaccine-induced thrombosis and thrombocytopenia (VITT) and heparin-induced thrombocytopenia (HIT)?

The antibody in HIT is directed against a complex formed by PF4 (a plasma protein) and heparin. In VITT, the antibody targets PF4 or PF4-vaccine complex. The lab tests used for VITT are modifications of the tests traditionally used in HIT. The treatment for HIT is non-heparin anticoagulants, but VITT treatment comprises anticoagulant and IVIG (immunoglobulin infusion).

What are the potential mechanism of VITT?

The vaccine (or a component of it) combining with PF4 induces an intense immune response, producing an antibody that activates platelets, making them sticky and clump together leading to clot formation and a drop in blood platelet level.

Knowledge of its mechanism is vitally important. More research is needed.

If we can identify what it is in the vaccine that induces the immune reaction, the offending component can be substituted to prevent VITT. This will also inform on the potential of other vaccines causing this rare clotting condition and also aids future vaccine development which uses the same technology.