Thrombosis with thrombocytopenia syndrome following adenovirus vector-based vaccines to prevent COVID-19: Epidemiology and clinical presentation in Spain.

Background: We describe the epidemiological and clinical characteristics of thrombosis with thrombocytopenia syndrome (TTS) cases reported in Spain.

Methods: We included all venous or arterial thrombosis with thrombocytopenia following adenovirus vector-based vaccines (AstraZeneca or Janssen) to prevent COVID-19 disease between February 1st and September 26th, 2021. We describe the crude rate and the standardized morbidity ratio. We assessed the predictors of mortality.

Results: Sixty-one cases were reported and 45 fulfilled eligibility criteria, 82% women. The crude TTS rate was 4/1 000 000 doses and 14-15/1 000 000 doses between 30-49 years. The number of observed cases of cerebral venous thrombosis was 6-18 higher than the expected in patients younger than 49 years. Symptoms started 10 (interquartile range (IQR): 7-14) days after vaccination. Eighty percent (95% confidence interval (CI): 65%-90%) had thrombocytopenia at the time of the emergency department visit, and 65% (95% CI: 49%-78%) had D-dimer >2000 ng/mL. Patients had multiple location thrombosis in 36% and fatal outcome in 24% cases. A platelet nadir < 50 000/μL (odds ratio (OR): 7.4; CI 95%: 1.2-47.5) and intracranial hemorrhage (OR: 7.9; IC95%: 1.3-47.0) were associated with fatal outcome.

Conclusion: TTS must be suspected in patients with symptoms 10 days after vaccination and thrombocytopenia and/or D-dimer increase.