Pooled IVE in hospitalized patients swabbed within 7 days of symptom onset.

<p>CI, confidence interval; IVE, influenza vaccine effectiveness.</p>a<p>Site as a random effect.</p>b<p>Adjusted by week of symptom onset, age group, sex, hospitalization in the previous 12 months, presence of chronic conditions, and smoking habits.</p

2012-2013 Seasonal Influenza Vaccine Effectiveness against Influenza Hospitalizations: Results from the Global Influenza Hospital Surveillance Network

<div><p>Background</p><p>The effectiveness of currently licensed vaccines against influenza has not been clearly established, especially among individuals at increased risk for complications from influenza. We used a test-negative approach to estimate influenza vaccine effectiveness (IVE) against hospitalization with laboratory-confirmed influenza based on data collected from the Global Influenza Hospital Surveillance Network (GIHSN).</p><p>Methods and Findings</p><p>This was a multi-center, prospective, active surveillance, hospital-based epidemiological study during the 2012–2013 influenza season. Data were collected from hospitals participating in the GIHSN, including five in Spain, five in France, and four in the Russian Federation. Influenza was confirmed by reverse transcription-polymerase chain reaction. IVE against hospitalization for laboratory-confirmed influenza was estimated for adult patients targeted for vaccination and who were swabbed within 7 days of symptom onset. The overall adjusted IVE was 33% (95% confidence interval [CI], 11% to 49%). Point estimates of IVE were 23% (95% CI, −26% to 53%) for influenza A(H1N1)pdm09, 30% (95% CI, −37% to 64%) for influenza A(H3N2), and 43% (95% CI, 17% to 60%) for influenza B/Yamagata. IVE estimates were similar in subjects <65 and ≥65 years of age (35% [95% CI, −15% to 63%] vs.31% [95% CI, 4% to 51%]). Heterogeneity in site-specific IVE estimates was high (I² = 63.4%) for A(H1N1)pdm09 in patients ≥65 years of age. IVE estimates for influenza B/Yamagata were homogenous (I² = 0.0%).</p><p>Conclusions</p><p>These results, which were based on data collected from the GIHSN during the 2012–2013 influenza season, showed that influenza vaccines provided low to moderate protection against hospital admission with laboratory-confirmed influenza in adults targeted for influenza vaccination. In this population, IVE estimates against A(H1N1)pdm09 were sensitive to age group and study site. Influenza vaccination was moderately effective in preventing admissions with influenza B/Yamagata for all sites and age groups.</p></div

Characteristics of patients included in the IVE analysis according to vaccination the current year (2012–2013).

<p><i>P</i>-values were determined by Pearson’s chi-square test. NC, not calculated.</p>a<p>N = 2158.</p>b<p>N = 2032.</p>c<p>N = 1069.</p>d<p>No impairment defined as a Barthel score >60.</p>e<p>N = 2168.</p

Heterogeneity of IVE estimates at each site for each age group.

<p>Heterogeneity of IVE estimates at each site for each age group.</p

Heterogeneity of IVE estimates at each site overall.

<p>Heterogeneity of IVE estimates at each site overall.</p

RT-PCR results at each site overall and in patients 18–64 and ≥65 years of age.

a<p>Percentages are compared to the total of all patients in the category.</p>b<p>Percentages are compared to influenza-positive patients.</p

Heterogeneity of IVE estimates for each strain in patients 18–64 years of age.

<p>Heterogeneity of IVE estimates for each strain in patients 18–64 years of age.</p

Characteristics of patients included in the IVE analysis at each site.

a<p>Missing: St. Petersburg, n = 12; France, n = 1.</p>b<p>Missing: St. Petersburg, n = 11; France, n = 65.</p>c<p>Presented only for patients ≥65 years of age. No impairment defined as a Barthel score >60. Data missing: St. Petersburg, n = 13; Moscow, n = 37.</p

Number of admissions by epidemiological week at each site.

<p>The number of patients enrolled and included in the IVE analysis is shown by epidemiological week at each site for each influenza strain.</p

Subjects included and excluded by coordinating site.

<p>Subjects included and excluded by coordinating site.</p