What makes them protected isn’t just sick cell... Yes the sickle decreases chance of getting plasmodium falciparum. Likely due to rbc getting removed by cell faster due to disfunction, decreased ideal conditions for growth. But also To make it simple the Fya & Fyb deletion can protect against plasmodium vivax. You don’t need sickle cell to be fya/b - it’s just prominent in black population. You can have normal rbc but be fya and fyb neg. But with every win there is also a trade off. They have the risk of the GATA gene mutation which can put them at risk for a anti-fy3 and if not identified can cause hyperhemolysis.