Ongoing measles outbreak in Wallonia, Belgium, December 2016 to March 2017: characteristics and challenges., Grammens, Tine, Schirvel Carole, Leenen Sylvie, Shodu Nathalie, Hutse Veronik, da Costa Elise Mendes, and Sabbe Martine , Euro Surveill, 2017 Apr 27, Volume 22, Issue 17, (2017)