COVID-19 (Coronavirus disease 2019) is a public health emergency of international con-cern . There is a pressing urgency to find treatments based upon currently available scien-tific knowledge and epidemiological data . In this article, we provide a novel hypothesis describing how the severity of the pathology is mainly resulting from the Antibody responses to SARS-CoV-2 (virus causing COVID-19) and not due to the direct action of the virus . SARS-CoV-2 appears to alter the endothelial cell . The pathophysiological mecha-nism is not yet elucidated . The damage caused resembles a systemic, multi-organ vascu-litis predominantly in the lungs . An increase in thromboembolic complications has been observed in COVID-19 patients . These are manifested by pulmonary embolisms or systemic microembolism manifested by microangiopathy affecting the lungs, brain, liver, kidneys and intestines . Therefore, we hypothesize that an auto-immune acquired Protein S (PS) deficiency may be involved in the pathogenesis of thrombotic events in Covid-19 . Auto-antibodies to Protein S may form immune complexes, inducing increased clearance of PS or interfering with the protein C-protein S system . COVID-19 early thromboprophy-laxis in infected patients, or even effective anticoagulation, could prevent the progression to severe forms, thus reducing mortality in patients with COVID-19. Activated Protein C (APC), a physiological coagulation inhibitor with cytoprotective properties, could be an interesting avenue for the treatment of severe forms of the disease in intensive care; its administration in hypoxic patients could improve tissue oxygenation . Randomized resus-citation studies in patients with COVID19 are also needed to confirm our hypothesis.