Complex patterns of human antisera reactivity to novel 2009 H1N1 and historical H1N1 influenza strains

Background: During the 2009 influenza pandemic, individuals over the age of 60 had the lowest incidence of infection with approximately 25% of these people having pre-existing, cross-reactive antibodies to novel 2009 H1N1 influenza isolates. It was proposed that older people had pre-existing antibodies induced by previous 1918-like virus infection(s) that cross-reacted to novel H1N1 strains. Methodology/Principal Findings: Using antisera collected from a cohort of individuals collected before the second wave of novel H1N1 infections, only a minority of individuals with 1918 influenza specific antibodies also demonstrated hemagglutination-inhibition activity against the novel H1N1 influenza. In this study, we examined human antisera collected from individuals that ranged between the ages of 1 month and 90 years to determine the profile of seropositive influenza immunity to viruses representing H1N1 antigenic eras over the past 100 years. Even though HAI titers to novel 2009 H1N1 and the 1918 H1N1 influenza viruses were positively associated, the association was far from perfect, particularly for the older and younger age groups. Conclusions/Significance: Therefore, there may be a complex set of immune responses that are retained in people infected with seasonal H1N1 that can contribute to the reduced rates of H1N1 influenza infection in older populations. © 2012 Carter et al

Seropositive samples for influenza A strains.

<p>The percentage of serum samples that were HAI positive per decade of birth were identified for (A) historical Human H1N1 strains; 1934–1957, (B) contemporary Human H1N1 strains; 1986–2007, (C) Human H3N2 strains.</p

Schematic representation of influenza A subtypes circulating in the human population since 1918.

<p>Each subtype (colored boxes) and specific H1N1 strains used for analysis in this study are depicted chronologically.</p

Correlations of CA/07/09 antibody titers with titers for other H1N1 isolates.

<p>The rank-order correlation coefficient between the CA/07/09 HAI titer and each other H1N1 titer is displayed for each decade of birth. As indicated at the right of the figure, warmer colors correspond to higher correlation coefficients.</p

Fraction of sera positive for A/Mexico/4108/2009 (novel H1N1) influenza by HAI titer by decade of birth.

<p>The number of serum samples was categorized by HAI titer per age group. Dark blue = 1∶20; Light blue = 1∶40; Green = 1∶80; Yellow = 1∶160; Orange = 1∶320; Red = 1∶640.</p

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.</p

Impact of diabetes status on immunogenicity of trivalent inactivated influenza vaccine in older adults

Individuals with type 2 diabetes mellitus experience high rates of influenza virus infection and complications. We compared the magnitude and duration of serologic response to trivalent influenza vaccine in adults aged 50-80 with and without type 2 diabetes mellitus. Serologic response to influenza vaccination was similar in both groups: greater fold-increases in antibody titer occurred among individuals with lower pre-vaccination antibody titers. Waning of antibody titers was not influenced by diabetes status