Impact of Pneumococcal Vaccination on Nasopharyngeal Carriage of Streptococcus pneumoniae and Microbiota Profiles in Preschool Children in South East Poland

In 2017, Poland introduced the 10-valent pneumococcal conjugate vaccine (PCV) into its national immunization schedule. This prospective study was conducted between March and June 2020 to determine the impact of vaccination on prevalence of the nasopharyngeal carriage of S. pneumoniae in 176 healthy children and to determine how conjugate vaccines indirectly affect colonization of nasopharyngeal microbiota. Pneumococcal isolates were analyzed by serotyping and antimicrobial resistance tests. Nasopharyngeal microbiota were detected and identified using the culture method and real-time PCR amplification primers and hydrolysis-probe detection with the 16S rRNA gene as the target. In the vaccinated group of children, colonization was in 24.2% of children, compared to 21.4% in the unvaccinated group. Serotypes 23A and 23B constituted 41.5% of the isolates. Serotypes belonging to PCV10 and PCV13 constituted 4.9% and 17.1% of the isolates, respectively. S. pneumoniae isolates were resistant to penicillin (34.1%), erythromycin (31.7%), and co-trimoxazole (26.8%). Microbial DNA qPCR array correlated to increased amounts of Streptococcus mitis and S. sanguinis in vaccinated children, with reduced amounts of C. pseudodiphtericum, S. aureus, and M. catarrhalis. Introduction of PCV for routine infant immunization was associated with significant reductions in nasopharyngeal carriage of PCV serotypes and resistant strains amongst vaccine serotypes, yet carriage of non-PCV serotypes increased modestly, particularly serotype 23B.