In the present study, the antigenic model was integrated into the process of selecting vaccine strains for
H3N2 human influenza A virus. To imitate the real situation of selecting vaccine strains, the model parameters
were re-optimized for each target season using only the antigenic distances between the strains that were
isolated up to the end of pre-target season. Optimization was performed by minimizing the square sum of
residual errors in the estimates of antigenic distances using the genetic algorithm (Tomita et al., 2000).
Three sets of random real numbers were assigned as the initial parameter values to confirm the convergence
of the results (Suzuki, 2013b).