Researchers say the trait is extremely common because it used to have a beneficial effect; it protected people against a form of malaria that is now fairly rare.
Researchers aren’t yet clear on the mechanism by which the lack of Duffy antigens increases the risk of HIV infection, but they have a few theories. During an immune response, Duffy antigens create chemical messengers that summon white blood cells to fight an infection. Since those chemicals latch onto the same white blood cell proteins that are targeted by HIV, said Weiss, their absence in duffy-negative people may allow the virus to proceed unchecked [Wired News]. As for why HIV-infected patients with this genetic variant live longer, Weiss says it’s possible that since the white blood cells aren’t being summoned to the site of the infection, it may take longer for the HIV virus to spread throughout the body.
On the O blood type theory having better results with COVID (on a proportional basis). I believe There is something “there” in all of this yet to be discovered by scientists since an anti malaria drug seems to have some effect if given in the beginning
” While O blood types are more likely to get bitten by mosquitos, they are much less likely to develop severe Malaria; a trait which stems from the simplicity of the red blood cell surface coat.
https://www.news-medical.net/life-sciences/Malaria-A-Force-Shaping-Blood-Cell-Evolution.aspx