These basic principles of SARS-CoV-2 biochemistry and the associated key roles of the trillions of RBCs, platelets and endothelial cells in the average human adult, which have no ACE2 or (for endothelial cells) minimal ACE2 but very dense SA surface coatings, however, have been largely marginalized in most COVID-19 research of the past three years. Here, ACE2 is linked to COVID-19.