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Vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT)

Rare prothrombotic syndrome with thrombocytopenia and unusual-site thrombosis (cerebral venous, splanchnic) developing 4–30 days after adenoviral-vector COVID-19 vaccination, mediated by anti-PF4 antibodies, requiring nonheparin anticoagulation and intravenous immunoglobulin.

Written by: Saygı Hospital Health Guide Editorial Board
Last updated:

This content has been compiled by the Saygı Hospital Health Guide Editorial Board and is periodically reviewed by a specialist physician.

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What is Vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT)?

Vaccine-induced immune thrombotic thrombocytopenia (VITT), also called thrombosis with thrombocytopenia syndrome (TTS), is a rare immune-mediated prothrombotic disorder occurring approximately 4–30 days after adenoviral-vector SARS-CoV-2 vaccines (ChAdOx1, Ad26.COV2.S), mediated by autoantibodies against platelet factor 4 (PF4) that activate platelets via FcγRIIa.

Pathophysiology mimics autoimmune (heparin-independent) heparin-induced thrombocytopenia (HIT), with formation of immune complexes that activate platelets and induce widespread coagulation activation, often manifesting as cerebral venous sinus thrombosis, splanchnic vein thrombosis, or other unusual-site clots with concurrent thrombocytopenia.

Diagnosis requires combination of recent adenoviral-vector vaccination, thrombosis (commonly atypical site), thrombocytopenia, very high D-dimer, low fibrinogen, and positive anti-PF4 ELISA confirmed by functional assay (PF4-enhanced platelet activation test); rapid recognition and specific treatment are lifesaving.

Symptoms

Persistent severe headache 4–30 days post adenoviral-vector vaccination, often progressive and unresponsive to simple analgesia
Focal neurologic deficits, seizures, or impaired consciousness from cerebral venous sinus thrombosis
Abdominal pain, hepatosplenomegaly, or bowel ischemia from splanchnic (portal, mesenteric, hepatic) vein thrombosis
Leg swelling and pain (deep vein thrombosis), chest pain and dyspnea (pulmonary embolism)
Petechiae, ecchymoses, or mucosal bleeding from severe thrombocytopenia
Visual disturbances, papilledema, or signs of raised intracranial pressure

Risk Factors

Recent receipt of adenoviral-vector SARS-CoV-2 vaccine (ChAdOx1 nCoV-19 or Ad26.COV2.S) within the preceding 4–30 days
Younger age (under 50 years), with female predominance in some cohorts though not universal
Possibly underlying genetic susceptibility to PF4 autoantibody formation, similar to autoimmune HIT
First-dose vaccine exposure carries highest risk (subsequent doses with mRNA vaccines do not show increased risk)
No clear association with conventional thrombophilia, hormonal contraception, or prior COVID-19 infection
Population risk extremely low (estimated 1 per 50,000–100,000), so risk-benefit favored vaccine in most settings

When to See a Doctor?

If you experience any of the following symptoms, seek medical attention promptly:

  • New severe headache, neurologic symptoms, abdominal pain, leg swelling, or unusual bleeding 4–30 days after adenoviral-vector COVID-19 vaccine — emergency department evaluation with full blood count and D-dimer
  • Confirmed thrombocytopenia plus thrombosis post adenoviral-vector vaccine — urgent hematology and neurology consultation, hospitalization for VITT-specific treatment
  • Suspected cerebral venous sinus thrombosis with raised intracranial pressure or impending herniation — emergent neurosurgical and intensive care evaluation
  • Persistent or recurrent thrombosis on initial therapy — consideration of advanced immunomodulation and tailored anticoagulation
  • Long-term post-VITT follow-up patient — hematology surveillance, monitoring for recurrent thrombosis and antibody persistence

Treatment Methods

01
Avoid heparin and platelet transfusion (which may worsen thrombosis); use nonheparin anticoagulants such as argatroban, fondaparinux, danaparoid, or direct oral anticoagulants once stable
02
High-dose intravenous immunoglobulin (IVIG) 1 g/kg/day for 2 days to block FcγRIIa-mediated platelet activation
03
Corticosteroids (e.g., methylprednisolone or dexamethasone) as adjunctive immunomodulatory therapy
04
Therapeutic plasma exchange in severe or refractory cases, particularly with very high titer anti-PF4 antibodies and progressive disease
05
Multidisciplinary care including hematology, neurology, neurosurgery, and intensive care; long-term anticoagulation duration tailored to thrombosis site, recurrence risk, and antibody persistence (typically 3–12 months)

Which Department to Visit?

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