Epidemiology of Thrombotic Thrombocytopenia Syndrome 2011 to 2022: English Sentinel Network Cohort Studies

José M. Ordóñez-Mena, Debasish Kar, Xuejuan Fan, Filipa Ferreira, Sneha N. Anand, Deborah Layton, David Clifton, Mark Joy, Anshul Thakur, Anu Alessi, Andrew Lee, Lisa Mather and Simon de Lusignan ()
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José M. Ordóñez-Mena: University of Oxford
Debasish Kar: University of Oxford
Xuejuan Fan: University of Oxford
Filipa Ferreira: University of Oxford
Sneha N. Anand: University of Oxford
Deborah Layton: R&D, AstraZeneca
David Clifton: University of Oxford
Mark Joy: University of Oxford
Anshul Thakur: University of Oxford
Anu Alessi: R&D, AstraZeneca
Andrew Lee: AstraZeneca
Lisa Mather: R&D, AstraZeneca
Simon de Lusignan: University of Oxford

Drug Safety, 2025, vol. 48, issue 10, No 9, 1175 pages

Abstract: Abstract Background and Objective Thrombotic thrombocytopenia syndrome (TTS) is a rare condition following vaccination with adenovirus-vectored coronavirus disease 2019 (COVID-19) vaccines. This retrospective analysis of England primary care data aimed to estimate TTS event rates before, during, and after the COVID-19 pandemic, and following AZD1222 (ChAdOx1-nCoV-19) vaccination. Methods Primary care data on TTS events were collected using the Oxford-Royal College of General Practitioners Research and Surveillance Centre sentinel network. TTS events were defined as thromboembolism with coincident (± 7 days) thrombocytopenia events using Systematized Nomenclature of Medicine clinical terms (the current Brighton Collaboration definition could not be used in the study as data related to specific parameters [e.g., D-dimer or PF4 antibodies] were not available in the primary care database). Multivariable logistic regression analyses were performed to assess the association between covariates and TTS. Results Incident TTS rates per 100,000 person-years were: 0.42 in a pre-COVID-19 cohort (1 January, 2011–31 December, 2019; 9,062,313 individuals); 0 in 39,448 individuals with confirmed COVID-19 (1 July–31 December, 2020); 0.48 and 0.47 during the pre-vaccination pandemic period spanning 1 January–14 August, 2020 (13,245,710 individuals) and 15 August–31 December, 2020 (13,347,462 individuals); 2.41 in an AZD1222-vaccinated cohort (5,544,761 individuals; 1 January, 2021–4 July, 2022). Multivariable logistic regression analysis of TTS events (− 7/+ 42 days event-window; pre-COVID-19 cohort) showed greater odds in older individuals and high-risk groups as defined by the Joint Committee on Vaccination and Immunization. Thrombotic thrombocytopenia syndrome was rare in all cohorts. Differential covariate distributions precluded comparisons of TTS rates across cohorts. Covariate distributions within thromboembolism and thrombocytopenia cases were comparable to those of TTS cases. Conclusions Our study, using a previous definition of TTS, reinforces the very rare nature of TTS before and during the pandemic, and before and after the introduction of the AZD1222 vaccine; it also confirms the established very low incident event rate in individuals vaccinated with AZD1222.

Date: 2025
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DOI: 10.1007/s40264-025-01566-1

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