HbAS children had a lower risk of progression to symptomatic malaria once parasitemic than HbAA children at older ages. The y-axis on the left denotes the probability of developing symptomatic malaria in a given month if parasitemic. The y-axis on the right denotes the RR of symptomatic malaria once parasitemic. The light blue band indicates the 95% CI for the RR; protection is significant at the P = .05 level for ages where the band does not cross the dotted blue line. Data were analyzed using generalized estimating equations with robust inference.