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Epidemiological, immunological and virulence characteristics of persistent Streptococcus pneumoniae vaccine serotypes

Paige Skoko1,2, Sam Manna1,2,3, Laura K Boelsen1

  • 1Infection, Immunity and Global Health, Murdoch Children's Research Institute, Parkville, Australia.

Nature Communications
|May 15, 2026
PubMed

Insights

Pneumococcal conjugate vaccines (PCV) can select for less virulent strains of Streptococcus pneumoniae. Despite vaccine serotype persistence, post-vaccine lineages show reduced severity and drug resistance, indicating evolving bacterial populations.

Area of Science:

  • Microbiology
  • Immunology
  • Epidemiology

Background:

  • Streptococcus pneumoniae vaccine serotypes can persist after pneumococcal conjugate vaccine (PCV) introduction.
  • Understanding the evolutionary dynamics of these serotypes is crucial for assessing vaccine impact.

Purpose of the Study:

  • To examine the persistence and characteristics of specific Streptococcus pneumoniae serotypes (6A, 6B, 14, 19F, 23F) before and after PCV13 introduction in Mongolian children.
  • To evaluate the clinical and microbiological differences between pre- and post-vaccine pneumococcal lineages.

Main Methods:

  • Analysis of 6,545 nasopharyngeal swabs from children hospitalized with pneumonia.
  • Utilized DNA microarray to identify changes in serotype lineage composition over a six-year period.
  • Compared virulence and drug resistance profiles of pre- and post-PCV lineages.

Main Results:

  • Post-PCV lineages of serotypes 6B, 14, and 19F were associated with less severe pneumonia.
  • Post-PCV lineages of serotypes 6A, 6B, and 23F showed reduced multi-drug resistance compared to pre-PCV lineages.
  • The post-PCV lineage of serotype 6B exhibited lower capsule expression, thinner capsule, reduced antibody binding, and decreased virulence in mice.

Conclusions:

  • Pneumococcal conjugate vaccination may select for less virulent lineages within vaccine serotypes.
  • Evaluating the true value of vaccination requires considering factors beyond serotype prevalence, such as lineage-specific virulence.
  • Vaccination drives evolutionary changes in bacterial populations, necessitating ongoing surveillance and adaptive strategies.

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