Vaccine-induced immune thrombocytopenia and thrombosis (VITT) post-Covid-19 vaccination has been reported. This prothrombotic syndrome is also known as thrombosis with thrombocytopenia syndrome (TTS) and vaccine-induced prothrombotic immune thrombocytopenia (VIPIT). A prospective cohort study from the UK has characterized the clinical presentation and prognostic features of VITT associated with the Oxford-AstraZeneca ChAdOx1 nCoV-19 adenoviral vector vaccine.

This study published in the New England Journal of Medicine, is an analysis of the first 220 patients in the UK, aged 18-79 years, who presented to hospitals with suspected diagnosis of VITT between 22^nd March and 6^th June this year after the first dose of the Oxford-AstraZeneca vaccine. These patients had no known medical risk factors.

VITT was defined by the following five criteria: symptom onset 5 to 30 days after Covid-19 vaccination, presence of thrombosis, presence of thrombocytopenia (platelet count <150,000 per cu mm), d-dimer > 4000 fibrinogen-equivalent units (FEUs) and the presence of anti-platelet factor (PF)-4 antibodies. Participants who fulfilled all five of the aforementioned criteria were designated as having definite VITT, while patients in whom criterion was not met (usually because of missing data) were labelled as probable VITT. Based on these prespecified criteria, 170 patients were identified as definite VITT, while 50 were probable cases.

Results showed that VITT usually presented 5 to 30 days after the first dose of the Oxford-AstraZeneca vaccine. Although the rate of vaccination was higher in older adults given the focus on the elderly patients, most VITTs occurred in patients  younger than 60 years of age.

The predominant clinical presentation was cerebral venous thrombosis (50%) and 36% of patients with CVT had secondary intracranial hemorrhage.  The other presentations included VTE (DVT and PE), portal- and splanchnic-vein thrombosis and arterial events affecting the peripheral vasculature and the myocardial and cerebral arteries. Around 29% of patients had thrombosis at multiple sites.

The overall mortality rate was found to be 22%. The probability of death was higher 2.7 times in patients with cerebral venous sinus thrombosis, 1.7 times for every 50% decline in the baseline platelet count, 1.2 times for every rise of 10,000 fibrinogen-equivalent units in the baseline d-dimer level and 1.7 times for every 50% decrease in the baseline fibrinogen level. The mortality rate was 73% in patients with baseline platelet counts below 30,000 per cu mm and intracranial hemorrhage.

VITT has been reported to be a rare complication. Corroborating this, the study found that the  incidence of VITT, after the first dose, among persons younger than 50 years of age was 1:50,000, while in persons aged ≥50 years, the incidence was one per 100,000.

Thrombocytopenia along with low fibrinogen levels and higher d-dimer levels adversely affected prognosis. Mortality was highest in thrombocytopenic patients (platelet count <30,000 per cu mm), cerebral venous sinus thrombosis and intracranial hemorrhage.

VITT is a rare but potentially devastating complication that occurs after Covid-19 vaccination. This study has described clinical and laboratory risk factors for VITT in patients following the first dose of the Oxford-AstraZeneca vaccine. Patients should be educated about the need to be alert about symptoms such as new persistent headache, severe abdominal pain, leg pain, acute chest pain, dyspnea ≥5 days post-vaccine and seek immediate help in case such symptoms develop. Early identification of patients may help in timely initiation of anticoagulants and prevention of this catastrophic complication.¹

Reference

1. Pavord S, et al. Clinical features of vaccine-induced immune thrombocytopenia and thrombosis. N Engl J Med. 2021 Aug 11. doi: 10.1056/NEJMoa2109908.