Mid-season real-time estimates of seasonal influenza vaccine effectiveness in persons 65 years and older in register-based surveillance, Stockholm County, Sweden, and Finland, January 2017 Hergens, Maria-Pia and Baum, Ulrike and Brytting, Mia and Ikonen, Niina and Haveri, Anu and Wiman, Åsa and Nohynek, Hanna and Örtqvist, Åke, Eurosurveillance, 22, 30469 (2017), https://doi.org/10.2807/1560-7917.ES.2017.22.8.30469