Assessing the association between COVID-19 vaccination and thrombotic thrombocytopenia syndrome (ATTEST Study): Analyses of English data, 2020-2022.

Publication date: Dec 09, 2025

COVID-19 vaccine surveillance detected thrombotic thrombocytopenia syndrome (TTS), a rare combination of thrombosis and thrombocytopenia, after COVID-19 vaccination. We evaluated TTS risk within 28 days of AZD1222 and BNT162b2 exposure. Matched case-control (MCCS) and self-controlled case series (SCCS) studies used Oxford-Royal College of General Practitioners Research and Surveillance Centre data linked to immunisation, hospitalisation and death data. English patient records extracted from 2/12/2020 to 31/10/2022 were used to identify TTS cases and age, sex, and practice matched controls. Conditional logistic regression and conditional Poisson regression were used for MCCS and SCCS analyses, respectively. Of 666 TTS events identified, >90% happened without AZD1222/BNT162b2 exposure in the preceding 28 days. MCCS analyses showed no association between TTS and a composite of both first and second AZD1222 dose (adjusted odds ratio [aOR]: 1. 45 [95% CI: 0. 90-2. 34]). Both studies showed increased TTS risk after AZD1222 first dose (MCCS, aOR: 2. 12 [1. 14-3. 92]; SCCS, incidence rate ratio: 3. 49 [2. 22-5. 49]). No association between TTS and BNT162b2 was observed. Consistent with previous studies, we found an association between TTS and receiving a first dose of AZD1222. There were no associations of TTS with AZD1222 second dose and BNT162b2 first or second doses.

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