Emergence of antibiotic-resistant non-vaccine serotype pneumococci in nasopharyngeal carriage in children after the use of extended-valency pneumococcal conjugate vaccines in Korea

High rates of carriage caused by non-PCV13 serotypes such as 23A, 15B, and 15C that show nonsusceptibilities to penicillin and erythromycin were noted following the introduction of extended-valency PCVs in Korea.