Mestan EMEK, Gül ERGÖR, Emine AVCI, Mustafa DEMİRÖZ, Can Hüseyin HEKİMOĞLU, Selmur TOPAL

Seasonal Influenza Vaccine Effectiveness in Preventing Laboratory Confirmed Influenza in 2014-2015 Season in Turkey: A Test-Negative Case Control Study

Background: Influenza has an important publichealth impact worldwide with its considerable annualmorbidity among persons with or without risk factorsand its serious complications among persons in high-riskgroups. The seasonal influenza vaccine is essential forpreventing the burden of influenza in a population. Sincethe vaccine is reformulated each season according to thevirus serotypes in circulation, its effectiveness can varyfrom season to season. Vaccine effectiveness is definedas the relative risk reduction in vaccinated individuals inobservational studies.Aims: To calculate influenza vaccine effectiveness inpreventing laboratory-confirmed influenza in the Turkishpopulation for the first time using the national sentinelsurveillance data in the 2014-2015 influenza season.Study Design: Test-negative case-control study.Methods: We compared vaccination odds of influenzapositive cases to influenza negative controls in thenational influenza surveillance in Turkey to estimateinfluenza vaccine effectiveness.Results: The influenza vaccine effectiveness againstinfluenza A (H1N1) (68.4%, 95% CI: -2.9 to 90.3) andB (44.6%, 95% CI: -27.9 to 66.6) were moderate, andthe influenza vaccine effectiveness against influenza A(H3N2) (75.0%, 95% CI: -86.1 to 96.7) was relativelyhigh; all had low precision given the low vaccinationcoverage. Overall, the influenza vaccination coveragerate was 4.2% (95% CI: 3.5 to 5.0), which is not sufficientto control the burden of influenza.Conclusion: In Turkey, national surveillance forinfluenza should be strengthened and utilised annuallyfor the assessment of influenza vaccine effectiveness withmore precision. Annual influenza vaccine effectivenessin Turkey should continue to be monitored as part of thenational sentinel influenza surveillance.

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