OC 76.3 - SARS-CoV-2 vaccination and risk of Venous Thrombosis – Case Control study on routine care data from Dutch General Practitioners

Background: Conflicting results have been reported regarding the risk of a venous thrombotic event (VTE) after SARS-CoV-2 vaccination. Little is known about possible risk factors for vaccine-related VTE.

Aims: To determine the risk of VTE after SARS-CoV-2 vaccination and to determine whether there are subgroups of individuals who are particularly at increased risk of VTE after vaccination.

Methods: We performed a case-control study using routine care data. We selected, based on ICPC coding, free text and medication use, patients who had a first VTE in 2021 from general practitioners (GP) in the region of Leiden, the Netherlands. Controls were selected from the same GP database, with at least one contact with a GP in 2021, but without a VTE in 2021. Both cases and controls were aged 18 years and older.
Data on demographics, history of VTE, vaccination details (type and date of vaccination) and other VTE risk factor were extracted. After matching on calendar date (ratio cases: controls 1:3), odds ratios (OR) were estimated to assess the risk of VTE associated with SARS-CoV-2 vaccination, adjusted for age and sex. Vaccination was checked in the 28 days prior to the date of VTE or the matched date for their controls. A stratified analysis was performed for the risk of VTE.

Results: A total of 346 first VTE cases and 1038 controls were selected. Overall, SARS-CoV-2 vaccination was not associated with VTE risk (see table 1). However, after stratification for vaccine type, vector-based vaccines were associated with an increased risk, particularly for participants with high risk for VTE (OR: 2.8; 95%CI 1.0-7.7).

Conclusion(s): While overall no increased VTE risk was observed in 28 days after SARS-CoV-2 vaccination, results indicate that vector-based vaccines do increase the risk, particularly in the presence of other VTE risk factors.