Figure 2. Potential immunogenicity of emerging influenza A (H7N9) HA and HA from the current seasonal vaccine and H7 vaccines. The number of HLA ligands (putative T cell epitopes) per unit protein is plotted on an Immunogenicity Scale. This scale is correlated with observed immunogenicity in retrospective and prospective studies.^16,17 The numbers used in this scale reflect the difference between the number of predicted T cell epitopes we would expect to find in a protein of any given size by chance alone (based on an evaluation of more than 10,000 random protein sequences) and the number of putative epitopes predicted by the EpiMatrix System for a given protein. The EpiMatrix Protein Score of an “average” protein is zero. EpiMatrix Protein Scores above zero indicate the presence of excess MHC ligands and denote a higher potential for immunogenicity, while scores below zero indicate the presence of fewer potential HLA ligands than expected and a lower potential for immunogenicity. H7 has fewer HLA ligands than expected, which is reflected in its negative immunogenicity score. Seasonal strains of influenza are scored for potential immunogenicity on the left; their scores are much higher than H7N9.