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- Influenza vaccine effectiveness in Portugal: season 2014/2015 reportPublication . Machado, Ausenda; Ambrósio Rodrigues, Ana Paula; Guiomar, Raquel; Pechirra, Pedro; Nunes, Baltazar[eng] Background: The EuroEVA project is the Portuguese component of the multicentre I-MOVE study. The results to be presented are related to the 7th EuroEVA season and aimed the estimation of 2014-15 end of season influenza vaccine effectiveness in i) all age groups; ii) by risk group; iii) by influenza subtype and thus contribute to monitor VE estimates every year. Material and methods: The “Protocol for case-control studies to measure seasonal influenza vaccine effectiveness in the European Union and European Economic Area Member States- Portuguese site study version” was implemented entirely with no changes to be added. VE was estimated as one minus the odds ratio of being vaccinated in cases versus controls adjusted for confounders by logistic regression. Potential confounders were investigated and included if they changed crude OR estimate in at least 10% after adjustment by the Mantel-Haenszel method. Results: In Portugal, influenza epidemic occurred between week 1/2015 and week 8/2015 and had a medium- high intensity. Both B and A(H3) virus were circulating, but with dominance of the first one. A(H1)pdm09 was only detected sporadically. From the 50 GP’s that accepted to participate in the study, 31 GP’s effectively participated in the study by selecting patients (which corresponds to a 62% participation rate). A total of 268 ILI patients were enrolled, each GP recruited in average 8.6 patients. After excluding 19 ILI patients the final sample for analyses consisted on 249 ILI patients (147 cases and 102 controls). From the cases, 68% were positive for type B virus, Yamagata lineage, 31% were positive for influenza A (H3) and 1% for A(H1)pdm09. Antigenic and genetic analysis indicated that influenza A(H3) viruses were genetically and antigenically different from the 2014/2015 vaccine strain, most of them belonging to the new virus cluster 3C.2a. Detected influenza B viruses belong to the same lineage (Yamagata) of the strain represented in the 2014/2015 influenza vaccine. Comparing cases and controls, we verified that they were statistically different in relation to: - Age: controls were older than cases (median age in controls was 51 yrs vs. 44 yrs in cases); - Any chronic disease: the prevalence of at least one chronic condition relevant for influenza vaccination was higher in controls (44.1% vs 28.1%); - Seasonal vaccine in 2013-14: controls were more often vaccinated against influenza in the last season than cases (28.4% vs. 12.3%); - Help bathing: controls needed more help for bathing than cases (0% in cases vs 4.1% in controls). Overall results indicated that vaccine coverage (VC) in controls was statistically higher (p<0.001) than in cases (VC controls=30.7% and VC cases=11.0%). Similar results were obtained for the target group for vaccination by the National Health Authorities (VC cases=26.8% and VC controls=54.9%, p=0.003). Restricting the analysis to type B virus (Yamagata lineage), VC was statistically (p=0.001) higher in controls than in cases (30.7% vs 8.1% in all ILI cases and 53.9% vs 20.0% in the target group). After adjustment for age, chronic disease and month of illness onset, VE adjusted estimates in all population was 63.4% (95% CI: 16.2%; 84.0%). In the target group for vaccination, after adjustment, VE estimates was 65.0% (95% CI: 8.1%; 86.7%). Restricting to B Yamagata cases, similar VE estimates were obtained for all population and target group: VE all population = 78.5% (95% CI: 39.5; 92.4); VE target group = 79.6% (95CI: 34.7; 93.6). Although all crude and adjusted VE estimates were statistically significant, low precision was observed. Conclusions: The 2014-2015 season adjusted VE estimates against B/Yamagata was approximately 79% (statistically significant but low precision). No VE estimates against A(H3) were obtained due to small sample size. All influenza B belonged to genetic group 3, different from genetic group 2, represented by B/Massachusets/02/2012 vaccine strain but antigenically these strains are related. This fact is in line with a moderate/high VE for influenza B in 2014-15 season.