Abstract
Hereditary protein S (PS) deficiency is a rare condition associated with increased risk of venous thromboembolism (VTE). In 2020, the coronavirus disease 2019 (COVID-19) pandemic prompted development of vaccinations to protect against the virus. PS deficiency is not a contraindication to COVID-19 vaccinations, but there are no studies regarding potential adverse effects in this population. We report two cases, a 43-year-old mother and her 18-year-old son, who developed VTE shortly after their first COVID-19 vaccines. Testing confirmed hereditary PS deficiency with a previously undescribed mutation in both cases. The temporal association between COVID-19 vaccination and VTE in these patients with hereditary PS deficiency suggests a potential causal relationship. However, it is unclear if this applies to all patients with hereditary PS deficiency. This highlights the importance of reporting adverse events following COVID-19 vaccinations in this population to evaluate the risks and benefits of vaccination.