Comparisons of pre-existing high risk conditions of children hospitalized for influenza A pH1N1 with age- matched controls hospitalized for seasonal H1N1 and H3N2, and with children hospitalized for seasonal influenza concurrently during the study period, respectively.

<p>Comparisons of pre-existing high risk conditions of children hospitalized for influenza A pH1N1 with age- matched controls hospitalized for seasonal H1N1 and H3N2, and with children hospitalized for seasonal influenza concurrently during the study period, respectively.</p

Comparison of clinical diagnosis of children hospitalized for influenza A pH1N1 with age- matched controls hospitalized for seasonal H1N1 and H3N2, and with children hospitalized for seasonal influenza concurrently during the study period, respectively.

<p>Comparison of clinical diagnosis of children hospitalized for influenza A pH1N1 with age- matched controls hospitalized for seasonal H1N1 and H3N2, and with children hospitalized for seasonal influenza concurrently during the study period, respectively.</p

Bias, RMSE of the estimated excess hospitalization rates from the observed hospitalization rates with laboratory confirmed influenza infections.

<p>Note. QAIC, quasi-Akaike information criterion; QBIC, quasi-Bayesian information criterion; PACF, partial autocorrelation function; GCV, generalized cross validation; RMSE, root-mean-square error.</p

Percentage difference of estimated excess hospitalization rates from the observed admission rates of influenza cases during 2003−2008.

<p>Note: Percentage difference = 100%× (estimated excess hospitalization rate – observed rate)/observed rate.</p

Weekly observed all-cause mortality (black line) and simulated mortality data (green lines).

<p>Data were generated (A) under the assumption of low seasonal variation with the degree of freedom for trend set at 1 per year, or (B) under the assumption of high seasonal variation with the degrees of freedom for trend set at 10 per year.</p

Bias, Standard error and RMSE of influenza coefficients estimated from the best-fit models selected by different criteria.

<p>Note: Lines of QAIC and QBIC are overlapping when the degrees of freedom (<i>df</i>) range from 2 to 10 per year. Abbreviations: QAIC, quasi-Akaike information criterion; QBIC, quasi-Bayesian information criterion; PACF, partial autocorrelation function; GCV, generalized cross validation; RMSE, root-mean-square error.</p

The Effect of Age and Recent Influenza Vaccination History on the Immunogenicity and Efficacy of 2009–10 Seasonal Trivalent Inactivated Influenza Vaccination in Children

<div><p>Background</p><p>There is some evidence that annual vaccination of trivalent inactivated influenza vaccine (TIV) may lead to reduced vaccine immunogenicity but evidence is lacking on whether vaccine efficacy is affected by prior vaccination history. The efficacy of one dose of TIV in children 6–8 y of age against influenza B is uncertain. We examined whether immunogenicity and efficacy of influenza vaccination in school-age children varied by age and past vaccination history.</p> <p>Methods and Findings</p><p>We conducted a randomized controlled trial of 2009–10 TIV. Influenza vaccination history in the two preceding years was recorded. Immunogenicity was assessed by comparison of HI titers before and one month after receipt of TIV/placebo. Subjects were followed up for 11 months with symptom diaries, and respiratory specimens were collected during acute respiratory illnesses to permit confirmation of influenza virus infections. We found that previous vaccination was associated with reduced antibody responses to TIV against seasonal A(H1N1) and A(H3N2) particularly in children 9–17 y of age, but increased antibody responses to the same lineage of influenza B virus in children 6–8 y of age. Serological responses to the influenza A vaccine viruses were high regardless of vaccination history. One dose of TIV appeared to be efficacious against confirmed influenza B in children 6–8 y of age regardless of vaccination history.</p> <p>Conclusions</p><p>Prior vaccination was associated with lower antibody titer rises following vaccination against seasonal influenza A vaccine viruses, but higher responses to influenza B among individuals primed with viruses from the same lineage in preceding years. In a year in which influenza B virus predominated, no impact of prior vaccination history was observed on vaccine efficacy against influenza B. The strains that circulated in the year of study did not allow us to study the effect of prior vaccination on vaccine efficacy against influenza A.</p> </div

Antigenic relationship between vaccine virus strains included in the trivalent inactivated influenza vaccines for the 2007–2010 seasons (Northern Hemisphere).

<p>Antigenic relationship between vaccine virus strains included in the trivalent inactivated influenza vaccines for the 2007–2010 seasons (Northern Hemisphere).</p

Individual antibody titers before and one month after receipt of trivalent inactivated influenza vaccine (TIV) in 2009–2010 among 6–8 y (Y, represented by blue circles) and 9–17 y children (O, represented by grey circles) with regard to their vaccination history for the 2007–2008 and 2008–2009 seasons.

<p>The median and interquartile range of antibody titers are shown, p-values were obtained by non parametric Wilcoxon signed rank tests. The comparisons were made with reference to children who were randomized to receive TIV in 2009–10 but did not receive any TIV during 2007–2008 and 2008–2009 seasons. The two p-values shown in each plot were obtained by comparison with children of the same age in the corresponding reference group (6–8 y and 9–17 y).</p

Characteristics of 479 subjects randomized to receive trivalent inactivated influenza vaccine (TIV) in 2009–10 with regard to their vaccination history in 2007–08 and 2008–09.

<p>Characteristics of 479 subjects randomized to receive trivalent inactivated influenza vaccine (TIV) in 2009–10 with regard to their vaccination history in 2007–08 and 2008–09.</p