Rise of multidrug-resistant Streptococcus pneumoniae clones expressing non-vaccine serotypes among children following introduction of the 10-valent pneumococcal conjugate vaccine in Bulgaria

Clonality was found behind the wide distribution of MDR capsular types 19A, 6C, 23A and 3 following vaccine introduction, and a highly multiresistant and virulent clone Taiwan19F-14/ST320 has emerged as a common pathogen in children.