Challenges of Maintaining Polio-free Status of the European Region. - Khetsuriani, Nino; Pfeifer, Dina; Deshevoi, Sergei; Gavrilin, Eugene; Shefer, Abigail; Butler, Robb; Jankovic, Dragan; Spataru, Roman; Emiroglu, Nedret; Martin, Rebecca (Journal of Infectious Diseases, 2014)