Duffy phenotypes were determined for 314 Malaysian Orang Asli. The most common gene, Fya, was present in 313; there were no Duffy negative individuals. A previous study found evidence of Plasmodium vivax infection in 5 of 7 Orang Asli reported to be of the Duffy negative genotype. In this study, 5 of the 7 previously tested Orang Asli were retested in triplicate, and each of the 5 was found to be Duffy positive, having the Fya gene and a phenotype of Fy (a + b-).
A double blind, randomized, controlled Phase 2 clinical trial was conducted to assess the safety, immunogenicity, and biologic impact of the vaccine candidate Apical Membrane Antigen 1-Combination 1 (AMA1-C1), adjuvanted with Alhydrogel. Participants were healthy children 2-3 years old living in or near the village of Bancoumana, Mali. A total of 300 children received either the study vaccine or the comparator. No impact of vaccination was seen on the primary endpoint, the frequency of parasitemia measured as episodes >3000/microL/day at risk. There was a negative impact of vaccination on the hemoglobin level during clinical malaria, and mean incidence of hemoglobin <8.5 g/dL, in the direction of lower hemoglobin in the children who received AMA1-C1, although these differences were not significant after correction for multiple tests. These differences were not seen in the second year of transmission.