Studies have shown that those with type A and AB blood have been found to have an increased risk of contracting COVID compared to someone with type O or B blood. This theory has been supported based off of statistical data which describes number of positive COVID cases and severity across the various blood types. It has been found that those with type A or AB blood run a higher risk of infection than type O or B.
This idea cannot be used to allocate how the population should consider precautions however. This theory although is interesting in tracking risk, could prove to be detrimental to ultimately gaining control of the rate of infection. If the knowledge that type O and B persons are at a lesser risk of contracting COVID, they could potentially loosen their constraints on recent social restrictions and proper masking.
https://www.nature.com/articles/s41467-020-19623-x
