Hospital-Based Surveillance of Pediatric Invasive Pneumococcal Diseases, 2016-2023 in Korea: Serotype Trends and Vaccination Policy.

Background: In Korea, the 10-valent and 13-valent pneumococcal conjugate vaccines (PCVs) were introduced into the national immunization program (NIP) in 2014 for the protection in children. A decade later, in 2024, PCV15 replaced PCV10 and was included in the NIP in April, while PCV20 was licensed for use in October. To inform optimal vaccination policy, this study aimed to analyze the current distribution of serotypes responsible for invasive pneumococcal diseases (IPDs) in children.

Methods: IPD cases from children under 19 years of age were collected from a prospective hospital-based surveillance study conducted at 20 hospitals between 2016 and 2023. Data on the changes in IPD case number and serotype distribution were compared between the pre- coronavirus disease 2019 (COVID-19) period (2016-2019) and the during/post-COVID-19 period (2020-2023).

Results: Of the 187 cases with a determined serotype, the most frequent serotypes identified were 10A (21.9%), 15C (11.8%), 15A (9.1%), 15B (8.0%), and 19A (7.5%), and 23B (5.9%). Compared to the pre-COVID-19 period, the proportion of serotype 10A decreased (27.4% vs. 12.9%), while serotypes 23B (0.9% vs. 14.3%) and 6C (0.9% vs. 7.1%) increased. In regard to the vaccine serotype, PCV13 serotypes accounted for 12.3%, PCV15/PCV20 common serotypes for 3.2%, and PCV20 unique serotypes for 35.3% of IPD cases. Serotype 15C, cross protected by the 15B conjugate vaccines, accounted for 11.8%, and non-PCV20 serotypes for 36.4%.

Conclusion: Given the approval of two new PCVs, the study results identified the substantial contribution of non-PCV13 serotypes to pediatric IPD and provide critical insights for optimal vaccination strategies to protect children against pneumococcal diseases.