Seropositivity (HAI≥1∶40) for multiple seasonal H1N1 influenza viruses 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 for ≥4 seasonal H1N1 (red) or positive for <4 seasonal H1N1 (blue). Panel (B): The percentage of serum samples positive for ≥4 seasonal H1N1 influenza viruses among those that were positive (red) or negative (blue) for A/California/07/2009 (novel H1N1) influenza. Panel (C): Odds ratio for seropositivity for A/California/07/2009 and seropositivity for ≥4 seasonal H1N1 influenza viruses. In all three panels the error bars indicate 95% confidence intervals.