This pilot study will seek to find biomarkers for blood clot risks in patients who have been given the AstraZeneca COVID-19 vaccine. Patients will be screened 10 days after their first injection to determine their risk of developing a rare blood clot from the vaccine. This study will help increase understanding of why some people are more susceptible to blood clotting, which could allow them to take a preventative treatment to protect them from blood clots.