The first study (Chinese) that showed people with Blood group O to be about 20% less likely to be infected by C19 than other blood groups. Other recent studies seems to show this is correct. O is common in Africa, SEA, and almost exclusive in the Amazon. medrxiv.org/content/10.110…
O also protects against malaria, but on the flipside, O is the most susceptible blood type to norovirus, which is far more common than C19 and kills about 200,000 every year, worldwide, many of them children.
However, blood groups can't be a major factor in infection rates, since both Germany and Japan are doing well with a majority A type population (A seems to be the most C19 susceptible group).
