Effectiveness of the 2010-11 seasonal trivalent influenza vaccine in Spain: cycEVA study.

BACKGROUND: In Spain, the influenza vaccine effectiveness (VE) was estimated in the last three seasons using an observational study (cycEVA) conducted in the frame of the Spanish Influenza Sentinel Surveillance System. We aimed to measure the effectiveness of the seasonal trivalent vaccine in preventing influenza like illness (ILI) laboratory-confirmed influenza infection at the end of the season 2010-11. METHODS: We conducted a test-negative case-control study between weeks 50/2010 and 12/2011. Cases were ILI laboratory-confirmed influenza infection and controls were those testing negative. Sentinel physicians collected data on demographic and clinical characteristics, vaccination status, and on covariates related to confounding factors associating with influenza VE. We calculated adjusted odds ratios (OR), using logistic regression and computed influenza VE as (1-OR) × 100. RESULTS: The adjusted influenza VE against A(H1N1)pdm09 infection was 46% (95% confidence interval (95%CI): 0; 72). In A(H1N1)pdm09 infected patients who had received both 2010-11 trivalent influenza seasonal and 2009 monovalent pandemic vaccines, influenza VE was 74% (95%CI: 13; 93). The adjusted influenza VE against B infection was 23% (95%CI: -180; 79). CONCLUSION: The trivalent influenza vaccine 2010-11 showed a moderate VE for preventing ILI laboratory confirmed influenza infections. Influenza VE estimates were higher in patients who had received both 2010-11 seasonal trivalent and 2009 monovalent pandemic vaccines.

Effectiveness of the 2010/11 seasonal trivalent influenza vaccine in Spain: preliminary results of a case-control study.

We present preliminary results of a case-control study to estimate influenza vaccine effectiveness in Spain, from week 50 of 2010 to week 6 of 2011. The adjusted effectiveness of the vaccine in preventing laboratory-confirmed influenza due to any type of influenza virus was 50% (95% CI: -6 to 77%) for the trivalent seasonal vaccine and 72% (95% CI: 7 to 92%) for both trivalent seasonal and monovalent pandemic vaccines, suggesting a protective effect of seasonal vaccination lower than that reported for the previous season.

"I-MOVE" towards monitoring seasonal and pandemic influenza vaccine effectiveness: lessons learnt from a pilot multi-centric case-control study in Europe, 2008-9.

Within I-MOVE (European programme to monitor seasonal and pandemic influenza vaccine effectiveness (IVE)) five countries conducted IVE pilot case-control studies in 2008-9. One hundred and sixty sentinel general practitioners (GP) swabbed all elderly consulting for influenza-like illness (ILI). Influenza confirmed cases were compared to influenza negative controls. We conducted a pooled analysis to obtain a summary IVE in the age group of >or=65 years. We measured IVE in each study and assessed heterogeneity between studies qualitatively and using the I2 index. We used a one-stage pooled model with study as a fixed effect. We adjusted estimates for age-group, sex, chronic diseases, smoking, functional status, previous influenza vaccinations and previous hospitalisations. The pooled analysis included 138 cases and 189 test-negative controls. There was no statistical heterogeneity (I2=0) between studies but ILI case definition, previous hospitalisations and functional status were slightly different. The adjusted IVE was 59.1% (95% CI: 15.3-80.3%). IVE was 65.4% (95% CI: 15.6-85.8%) in the 65-74, 59.6% (95% CI: -72.6 -90.6%) in the age group of >or=75 and 56.4% (95% CI: -0.2-81.3%) for A(H3). Pooled analysis is feasible among European studies. The variables definitions need further standardisation. Larger sample sizes are needed to achieve greater precision for subgroup analysis. For 2009-10, I-MOVE will extend the study to obtain early IVE estimates in groups targeted for pandemic H1N1 influenza vaccination.