Risk of Thrombosis with Thrombocytopaenia Syndrome (Tts) after Vaccination with Azd1222: A European Vac4eu Post-Authorisation Safety Study
Bibliographic record
Abstract
A post-authorisation safety study was conducted for the AZD1222 COVID-19 vaccine. This paper presents one study outcome, thrombosis with thrombocytopenia syndrome (TTS), and estimates TTS risk in subjects administered ≥1 AZD1222 dose versus concurrent unvaccinated, pre-pandemic historical, or mRNA-vaccinated subjects.The cohort study used data from CPRD Aurum (UK), VID (Spain), SIDIAP (Spain) and PHARMO-GP database (PHARMO) (the Netherlands). AZD1222-vaccinated subjects were matched on age, sex, region, prior COVID-19, and special population status. Incident venous TTS was defined as a thromboembolic event and thrombocytopaenia within ±10 days and no TTS within the prior year.5,321,930 subjects were matched with concurrent unvaccinated comparators, 4,831,010 with historical comparators, and 4,028,091 with mRNA active comparators (CPRD only). In CPRD, 83% of subjects were vaccinated in Q1 2021; 64% were <60 years. In VID, SIDIAP, and PHARMO, >59% were vaccinated after Q1 2021; most subjects were ≥60 years. Propensity score–weighted incidence rate ratios (IRRs) (95% confidence intervals) for TTS were CPRD, 1.14 (0.60-2.17); VID, 0.34 (0.10-1.18); SIDIAP, 0.66 (0.33-1.34); and zero events in PHARMO. Incidence rates (IRs) and IRRs for TTS, where available, were higher in AZD1222-vaccinated versus concurrent unvaccinated subjects <60 years or during shorter risk windows. After case validation, positive predictive value–adjusted IRRs were <1. For historical comparators, meta-analysis resulted in an IRR of 1.78 (95% CI,1.12-2.82; I2=0%). For mRNA active comparators, the IRR was 1.12 (95% CI,0.61-2.05).Considering the magnitude, precision, and potential biases—such as selection bias due to informative censoring and potential outcome misclassification—the totality of evidence suggests a possible increased risk of TTS with post-AZD1222 vaccination that may be higher among subjects <60 years and 1-42 days after first AZD1222 dose, in line with the literature. Differential age distributions resulting from country-level differences in the risk minimisation measures may explain IRR disparities across data sources.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.008 | 0.007 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".