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 cases of venous or arterial thrombosis with thrombocytopenia following administration of adenoviral vector vaccines (AstraZeneca or Janssen) against COVID-19 disease between 1 February and 26 September 2021. We describe the crude rate and the standardised morbidity ratio. We assessed the predictors of mortality.

Results: Sixty-one cases were reported and 45 fulfilled eligibility criteria; 82% of patients were women. The crude TTS rate was 4 cases/1 000 000 doses, and 14-15 cases/1 000 000 doses among patients aged 30-49 years. The number of observed cases of cerebral venous thrombosis was 6-18 times higher than that expected in patients younger than 49 years. Symptoms started a median (quartiles 1 and 3 [Q₁-Q₃]) of 10 (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% (49%-78%) had D-dimer levels > 2000 ng/mL. Patients had thromboses affecting multiple locations in 36% of cases and fatal outcomea in 24%. Platelet nadir < 50 000/μL (odds ratio [OR]: 7.4; 95% CI: 1.2-47.5) and intracranial hemorrhage (OR: 7.9; 95% CI: 1.3-47.0) were associated with fatal outcomes.

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