Seropositivity (HAI≥1∶40) for both novel H1N1 and 1918 influenza by decade of birth.

<p>Panel (A): The percentage of serum samples positive for A/California/07/2009 (novel H1N1) among those that were positive (red) or negative (blue) for 1918 influenza. Panel (B): The percentage of serum samples positive for 1918 influenza among those that were positive (red) or negative (blue) for A/California/07/2009 (novel H1N1) influenza. Panel (C): Odds ratio for seropositivity for the two antigens. In all three panels the error bars indicate 95% confidence intervals.