Evolving pneumococcal epidemiology and vaccine impact in the Netherlands, 2004-2024: Carriage and invasive disease

OBJECTIVES: Since pneumococcal conjugate vaccines (PCVs) were introduced into the Dutch childhood National Immunization Program in 2006, colonization and invasive disease of Streptococcus pneumoniae have declined, alongside shifts in serotype prevalence towards non-vaccine serotypes (NVTs). To monitor changes and estimate the added value of higher-valent PCVs, serotype-specific carriage, invasive pneumococcal disease (IPD) and invasive disease potential were analyzed. METHODS: During the winters of 2018/2019 and 2022/2023 pneumococcal carriage was determined among 24-month-old children and parents, and compared to carriage studies from 2005 to 2016. IPD data from Dutch surveillance (2004-2024) were included. Pneumococcal isolates were serotyped using agglutination and Quellung. Serotype-specific disease potential determined as odds ratios (OR) for IPD versus carriage. RESULTS: Pneumococcal carriage in children decreased from 66% in 2005 to 49% in 2018/2019 and 46% in 2022/2023. In 2022/2023, 29% of children carried NVTs, followed by PCV20- (11%), PCV13- (4%), PCV15- (2%) and PCV10- (0%) specific serotypes. Among parents, carriage declined from 17% in 2005 to 2% by 2022/2023. IPD incidence increased from 6·7 to 8·4 per 100,000 children under 5 years between 2018-2020 and 2022-2024, predominantly caused by an increase in serotype 19A. Serotypes 8 and 3 have the highest invasive disease potential. CONCLUSIONS: This study shows stabilized pneumococcal carriage from 2018 to 2023 with low invasive disease potential for common serotypes, except for serotype 19A. However, rising IPD incidence from other non-vaccine serotypes highlights the need for higher-valency vaccines. The newly introduced PCV15 covers 58% of IPD cases, while PCV20 could cover 73%.