The present invention relates to a protein composition suitable for inducing an immune response in a vertebrate comprising 2 to 10 protein variants of a single antigen, which is the APICAL MEMBRANE ANTIGEN 1 (PfAMA1 OR AMA1) of a Plasmodium species. The antigen comprises a plurality of variable amino acid positions, wherein the amino acid sequences of said protein variants, in combination, represent both the frequency of occurrence of each amino acid at said variable amino acid positions and the linkage between the variable amino acid positions, and wherein said frequency of occurrence is at least between 10% to 20% such as 10%, 11%, 12%, 13%, . . . , 20% in the single antigen, and wherein at least 75% of the linkages between the variable amino acid position is presented by the combination of protein variants.