Marks F, Nyambat B, Xu ZY, von Kalckreuth V, Kilgore PE, Seo HJ, Du Y, Park SE, Im J, Konings F, Meyer CG, Wierzba TF, Clemens JD. Vaccine introduction in the Democratic People's Republic of Korea. Vaccine. 2015 May 11; 33(20):2297-300.