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Stability of the pneumococcal population structure in Massachusetts as PCV13 was introduced

Qiuzhi Chang1, Abbie E Stevenson2, Nicholas J Croucher3,4

  • 1Department of Epidemiology, Harvard School of Public Health, 677 Huntington Avenue, Boston, MA, USA. qic716@mail.harvard.edu.

BMC Infectious Diseases
|April 19, 2015
PubMed

Insights

The 13-valent pneumococcal conjugate vaccine (PCV-13) showed initial impacts on pneumococcal serotype and sequence type (ST) frequencies in Massachusetts children in 2011. Further studies will track the long-term evolution of the pneumococcal population.

Area of Science:

  • Microbiology
  • Immunology
  • Epidemiology

Background:

  • The 7-valent pneumococcal conjugate vaccine (PCV-7) led to increased disease from non-vaccine serotypes, like 19A.
  • The 13-valent pneumococcal conjugate vaccine (PCV-13) was introduced in 2010 to address these limitations.

Purpose of the Study:

  • To assess the initial impact of PCV-13 introduction on the pneumococcal population in Massachusetts.
  • To analyze changes in pneumococcal serotypes and sequence types (STs) following PCV-13 implementation.

Main Methods:

  • Multilocus sequence typing (MLST) was used to analyze 367 pneumococcal isolates from children aged 3 months to 7 years.
  • eBURST software compared pneumococcal population structure to previous years, specifically a 2009 sample.

Main Results:

  • 104 distinct sequence types (STs) were identified, including 24 novel STs.
  • No significant overall change in ST composition was observed compared to 2009 (p=0.39).
  • Clonal dynamics were noted in serotypes 19A, 15B/C, and 6C, with expansion of ST 433 (serotype 22F) and ST 432 (serotype 21).

Conclusions:

  • While overall serotype and ST composition showed little change, shifts in individual ST and serotype frequencies may be linked to PCV-13 introduction.
  • This 2011 data provides a baseline for understanding the ongoing evolution of the pneumococcal population in response to PCV-13.
Abstract

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