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

BackgroundIn 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.MethodsWe 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.ResultsThe 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).ConclusionThe 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.

► 2010–11 influenza vaccine shows moderate effectiveness against confirmed cases.
► There is a higher protection in vaccinated with seasonal 2010–11 and pandemic 2009–10.
► Intra-seasonal estimates were similar to end-season one.
► cycEVA study provides yearly estimates contributing to national public health policy.