The post-vaccine microevolution of invasive Streptococcus pneumoniae

Area of Science:

• Microbiology
• Genomics
• Epidemiology

Background:

• The 7-valent pneumococcal conjugated vaccine (PCV7) impacts Streptococcus pneumoniae in children.
• Pneumococcal population genomics in adults with invasive pneumococcal disease (IPD) under vaccine pressure is poorly understood.

Purpose of the Study:

• To investigate pneumococcal population genomics in adult IPD strains before and after PCV7 introduction.
• To identify genetic changes and serotype replacement in Streptococcus pneumoniae following PCV7 implementation.

Main Methods:

• Whole genome sequencing and serotyping of 349 Streptococcus pneumoniae strains from adult IPD patients (2001-2011).
• Comparative genomic analysis to assess population structure and gene diversity changes.

Main Results:

• PCV7 introduction in 2006 led to significant alterations in IPD population structure, driven by serotype replacement.
• No evidence of vaccine-induced capsular switching was observed.
• A temporary bottleneck in gene diversity was followed by re-expansion, primarily with pre-PCV7 circulating genes.
• Post-vaccine, gene frequencies shifted, with some genes overrepresented in vaccine serotypes and others in non-vaccine serotypes.

Conclusions:

• Pneumococcal population genomics in adult IPD are significantly altered by PCV7, primarily through serotype replacement.
• Whole genome sequencing is crucial for surveillance of pneumococcal population dynamics, aiding IPD prevention and management.