Table 1. European Medicines Agency (EMA) immunogenicity criteria for annual licensing of influenza vaccine using HI (haemagglutinin inhibition) and SRH (single radial haemolysis) methods (9).

Criteria	Definition	≥60 years
Seroconversion or significant increase rate	HI method: Percentage of vaccines with pre-vaccination titre <10 and post-vaccination titre of ≥40 OR ≥10 and at least 4-fold rise in post-vaccination titre SRH method: Percentage of vaccines with negative pre-vaccination titre and post-vaccination area ≥25 mm2 OR ≥50% increase in area post-vaccination	>30%
Seroprotection	Percentage of vaccinees achieving post-vaccination HI titre of ≥40 OR SRH titre > 25 mm2	>60%
Mean geometric increase	Post / prevaccination GMT ratio	>2.0