Background: Vaccine-induced thrombotic thrombocytopenia, especially in unusual sites such as cerebral venous sinus thrombosis (CVST) is a rare adverse event following adenoviral vector-based COVID-19 vaccination.
Objectives: This study evaluated the short-term risk of CVST without thrombocytopenia after ChAdOx1 nCoV-19 vaccination.
Methods: Using the National Health Insurance Service database linked to the national COVID-19 vaccination database in Korea, we conducted an extended self-controlled case series study for event-dependent exposure. Eligible population were both unvaccinated and vaccinated patients, aged 19 years and older, hospitalized for CVST without thrombocytopenia, and underwent imaging studies such as magnetic resonance imaging or magnetic resonance venography. Patients were excluded if they had a history of CVST or trauma prior to index CVST, they were administered with BNT162b2 or mRNA-1273 vaccine, and they were diagnosed with COVID-19 during observation period. The risk periods were defined as the period of days 1 through 28 following the first or second dose of vaccine and the remaining periods as control periods. Unbiased estimating equations were used to estimate the relative incidences (RIs) and their 95% confidence intervals.
Results: A total of 170 patients were admitted for CVST without thrombocytopenia for a 304-day observation period stretching from January 1, 2021 to October 31, 2021. Among them, 64 were vaccinated at least one dose of ChAdOx1 nCoV-19 vaccine during observation period. The RI for CVST without thrombocytopenia following the first dose was 2.42 (95% CI, 1.11-5.28), following the second dose 1.82 (95% CI, 0.66-5.05), and following both doses 2.25 (95% CI, 1.11-4.55). By age group, the RI was highest in the 30-49 years age group (9.24; 95% CI, 0.95-89.57), and it was higher in women (2.93; 95% CI, 1.03-8.32) than in men (2.07; 95% CI, 0.82-5.19).
Conclusions: In this nationwide study, the increased risk of CVST without thrombocytopenia was observed within 28 days of risk intervals following ChAdOx1 nCoV-19 vaccination. Further investigations are needed to evaluate the diagnostic validity for identifying CVST and to confirm the results of this study.
