GP consultations for venous thromboembolism (VTE) after mRNA and adeno-vector-based COVID-19 vaccination - an exposure-anchored self-controlled cohort study based on pimary healthcare data from the Netherlands.

Introduction
Venous thromboembolism (VTE) is labeled as an adverse effect of the adeno-vector-based vaccines AstraZeneca and Johnson & Johnson. We aimed to study whether there was an increase in general practitioner (GP) consultations for VTE after COVID-19 vaccination.

Methods
An exposure-anchored self-controlled cohort study was performed among COVID-19 vaccinated persons aged ≥ 12 years who were registered in the PHARMO Data Network and Nivel Primary Care Database in the Netherlands. The focal window was set at 28 days after each COVID-19 vaccination and the referent window at all time outside the focal window. Adjusted incidence rate ratios (aIRR), adjusting for SARS-CoV-2 infection, were calculated using Poisson regression.

Results
In total, 2 133 853 persons were included. The highest increase in GP consultations for VTE was observed after Johnson & Johnson vaccination (aIRR: 3.14, 95% CI: 1.50-6.57), and a slight increase after Pfizer/BioNTech dose 1 (aIRR: 1.24, 95% CI: 1.09-1.40). Risk groups were 12-60 year-olds with increased GP consultations for VTE after Johnson & Johnson (aIRR: 2.30, 95% CI: 1.44-3.69) and Pfizer/BioNTech (aIRR: 1.29, 95% CI: 1.11-1.50), and in specific groups of males aged 12-60 years. Also, females using hormone-containing contraceptives or hormone replacement therapy (HRT) showed increased GP consultations for VTE after AstraZeneca (aIRR: 2.87, 95% CI: 1.13-7.33) and Pfizer/BioNTech (aIRR: 1.48, 95% CI: 1.10-2.01).

Conclusion
Increased GP consultations for VTE were observed after both vector and mRNA vaccination, in particular among males, 12-60 year olds, and females using hormone-containing contraceptives or HRT.