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The age-specific reproduction number Ra and the case distribution by age. In each subfigure we set the overall population R to the value shown, the ratio of susceptibility between adults (aged >20 years) and children (aged <20 years) to 1:5 and equal exposure of all age groups to swine. As the overall population R is raised from zero, in steps of 0.5 (from left to right), the figure shows the changing age distribution of cases and the age-specific reproduction number.
