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Streptococcus pneumoniae is a common cause of infectious diseases such as pneumonia and sepsis. Its colonization is thought to be the first step in the development of invasive pneumococcal diseases. This study aimed to investigate pneumococcal colonization patterns in early childhood. A longitudinal birth cohort study was conducted for investigating nasopharyngeal colonized pneumococci at 1, 6, 12, 18, 24, and 36 months of age, particularly focusing on the serotype distribution and antimicrobial susceptibilities. Pneumococcal conjugate vaccine (PCV) effect on nasopharyngeal colonization was also assessed. During 2013–2017, 855 infants were enrolled and a total of 107 isolates were recovered from 95 infants during the first three years of life. In this period, the prevalence of pneumococcal colonization increased, with values ranging from 0.2% (2/834) at 1 month of age to 5.9% (19/323) at 36 months of age. The investigation of serotype revealed that 81.1% (73/90) belonged to the non-PCV13 serotypes–23A, 15A, 15C, and 15B. Moreover, PCV13 serotypes significantly decreased during 2014–2015, when routine PCV13 vaccination was initiated in Taiwan. PCV13 introduction may lead to the reduction in the rates of pneumococcal isolates resistant (R) to penicillin. Under conditional PCV13 vaccination, pneumococcal isolates primarily belonged to non-PCV13 serotypes. This non-PCV13 serotype replacement exhibited lower rates of penicillin R isolates, suggesting that PCV13 administration may reduce the antibiotic-nonsusceptible pneumococcal disease burden and antibiotic use. [ABSTRACT FROM AUTHOR]