Can you please tell me why it'sthat only carriers of sickle cell anemia are immune to malaria?

Both carriers and : People with the disease are protected (not immune). People with trait historically were more likely to survive into adulthood to pass along the sickle cell gene. People with ss hemglobin, until recently, were not likely to survive into adulthood to have children.

Sickle Cell /Malaria: In a person who has sickle-cell trait – the red blood cells are destroyed prematurely before the Plamodium can reproduce. According to one study “Sickle cell trait provides 60% protection against overall mortality. Most of this protection occurs between 2-16 months of life, before the onset of clinical immunity in areas with intense transmission of malaria.”