Excellent question! Here's the answer: We have no idea! Blood type antigens are complex carbohydrates, and A/B/O is the difference between N-acetyl-Galactosam

Excellent question! Here's the answer: We have no idea! Blood type antigens are complex carbohydrates, and A/B/O is the difference between N-acetyl-Galactosamine/Galactose/nothing at the end of a sugar chain. So let's talk about Coronavirus and sugars. SARS-COV-2 (and the prequel for that matter) are relatively unique for viruses because they don't (as far as we know) use sugars (sialic acids to be specific) to bind to cells, unlike all of our other favourite viruses (e.g. influenza). BUT that's not the only place it could matter. Maybe sugars help organise the membrane to increase multivalent reactions, and there's some galectin that binds to B antigen. Or the virus itself somehow carries the antigen, and A/B protects against furin processing? Lots of possibilities. First thing I would check for is co-expression of ABO with ACE2. If it's not in the same cells, then I have NO idea how it works.