The difference in types is due to antigens, blobs of protein on the surfaces of the red blood cells. Type O has no A or B. Rh negative has no Rh antigen. O negative therefore has no antigens and AB positive has three. These antigens, if present, can interact with the SARS-2 Corona virus, like doubling exposure. It isn't that O is protective, but A and B add to the risk.
Here is the scholarly study: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7537232/
The difference in types is due to antigens, blobs of protein on the surfaces of the red blood cells. Type O has no A or B. Rh negative has no Rh antigen. O negative therefore has no antigens and AB positive has three. These antigens, if present, can interact with the SARS-2 Corona virus, like doubling exposure. It isn't that O is protective, but A and B add to the risk.