The Clinicalpathological Features of Vaccine-Induced Immune Thrombocytopenia and Thrombosis (VITT) Following ChAdOx1 (AstraZeneca AZD1222) Vaccination and Case Outcomes in Australia

Background Vaccine-induced immune thrombocytopenia and thrombosis (VITT) associated with viral vector COVID-19 vaccines including ChAdOx1 (AstraZeneca AZD1222 vaccine) can result in significant morbidity and mortality. We report the clinicopathological features of VITT following ChAdOx1 vaccination and summarise the case outcomes in Australia.

Methods In this cohort study, patients diagnosed with VITT in Australia between 23 March and 31 December 2021 were identified according to predefined criteria. Case classification was adjudicated against Brighton Collaboration and Centres for Disease Control and Prevention (CDC), and verified by the Therapeutic Goods Administration (TGA) vaccine team. Data were collected using standardised electronic case report forms. Patient baseline characteristics, clinicopathological features, risk factors, treatment and outcomes were recorded and analysed by case classification and clinical outcome.

Results A total of 170 probable or confirmed VITT cases were identified, most occurring after the first dose (87%) of ChAdOx1 vaccine. The median time to symptom onset after vaccination and symptoms onset to admission was 11 and 2 days respectively. The median age of cases was 66 years (interquartile range, 55-74). There was no sex preponderance and no medical risk factors were identified. All except two patients received therapeutic anticoagulation and 66% received intravenous immunoglobulin (IVIg). Overall, 85% of cases recovered (discharged home after a median hospitalisation of 6 days) and 9% required ongoing rehabilitation. The mortality rate was 6%, with the risk factors for death from VITT being presentation with cerebral venous sinus thrombosis or splanchnic vein thrombosis, haemorrhage both at presentation and during admission, and a lower initial or nadir platelet count.

Conclusion In this Australian cohort, VITT occurred predominantly after dose of ChAdOx1 COVID-19 vaccination. Clinician awareness and recognition of VITT, an efficient diagnostic pathway and prompt therapy with anticoagulation and IVIg has led to a high recovery rate and one of lowest mortality rates in the world.

Tran:Takeda: Speakers Bureau.