Impact of a pneumococcal conjugate vaccination program on carriage among children in Norway

Area of Science:

• * Pediatric infectious diseases
• * Vaccinology
• * Microbiology and immunology

Background:

• * The seven-valent pneumococcal conjugate vaccine (PCV7) was implemented in Norway in July 2006 using a 2-dose + 1 boost schedule.
• * Understanding post-vaccination pneumococcal dynamics is crucial for public health strategies.

Purpose of the Study:

• * To assess shifts in nasopharyngeal pneumococcal colonization reservoirs following PCV7 introduction.
• * To evaluate the impact of PCV7 on pneumococcal carriage prevalence and serotype distribution in children.

Main Methods:

• * Two point prevalence studies were conducted in day care centers in 2006 (pre-PCV7) and 2008 (post-PCV7).
• * Nasopharyngeal swabs from 1,213 children were analyzed for pneumococcal isolates (n=1,102).
• * Methods included serotyping, multilocus sequence typing, and antimicrobial susceptibility testing.

Main Results:

• * Carriage of PCV7 serotypes decreased in both vaccinated and unvaccinated children, indicating direct and indirect vaccine effects.
• * Overall pneumococcal carriage prevalence remained high at 80.4% after PCV7 introduction.
• * A shift towards non-PCV7 serotypes was observed, driven by the expansion of specific clonal complexes, without an increase in antimicrobial resistance among these emerging serotypes.

Conclusions:

• * PCV7 effectively reduced carriage of targeted serotypes, demonstrating both direct and indirect protection.
• * Pneumococcal populations adapted by increasing carriage of non-vaccine serotypes, maintaining overall high colonization levels.
• * The study did not find an increase in antimicrobial resistance associated with the replacement non-PCV7 serotypes.