Ongoing measles outbreak in Wallonia, Belgium, December 2016 to March 2017: characteristics and challenges Grammens, Tine and Schirvel, Carole and Leenen, Sylvie and Shodu, Nathalie and Hutse, Veronik and Mendes da Costa, Elise and Sabbe, Martine, Eurosurveillance, 22, 30524 (2017), https://doi.org/10.2807/1560-7917.ES.2017.22.17.30524