The direct impact of mandatory PCV10 vaccination on invasive pneumococcal disease in Polish children.

BACKGROUND

The introduction of pneumococcal conjugate vaccines (PCVs) into National Immunization Programs (NIP) has led to a significant decrease in pneumococcal infections. This study aimed to evaluate the direct impact of the introduction of PCV10 into the NIP in 2017 on the serotype distribution and antimicrobial susceptibility of pneumococci causing invasive pneumococcal disease (IPD) in Polish children.

METHODS

The study encompassed all pneumococcal strains responsible for IPD in Polish children under five years of age submitted to the reference centre between July 2013 and June 2023. Four analysis periods were defined: pre-PCV10 (July 2013-June 2016), early post-PCV10 (July 2017-June 2020), COVID-19 pandemic (July 2020-June 2021), and late post-PCV10 (July 2021-June 2023). Routine techniques were utilized for identification, serotyping, and antimicrobial susceptibility testing.

RESULTS

Following the introduction of PCV10, a significant decline in the proportion of IPD cases caused by PCV10 serotypes in children under five years of age was observed, decreasing from 52.1 % to 8.1 %. Also significant was a decrease of PCV10 serotypes among resistant pneumococci, including MDR isolates which dropped from 65.4 % to 9.8 %. In the late post-PCV10 period, isolates of serotype 19A (37.6 %) and serotype 3 (17.9 %) were the most prevalent. In the late post-PCV10 period, 19A pneumococci accounted for 77.0 % of all MDR cases.

CONCLUSIONS

The introduction of PCV10 into the Polish NIP significantly reduced infections caused by PCV10 serotypes, including infections associated with resistant pneumococci. Concurrently, we noted an increase in the prevalence of non-PCV10 serotypes, notably serotype 19 A, which presently constitutes one-third of the total infections. The results of our study support the need to introduce a vaccine containing 19A polysaccharides into the Polish NIP and emphasizes the importance of continuous IPD surveillance.