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Invasive pneumococcal isolates from Danish infants (0 - 90 Days) during the years 1943 to 2013

Hans-Christian Slotved1, Tine Dalby1, Steen Hoffmann1

  • 1Neisseria and Streptococcus Reference Laboratory (NSRlab), Department of Microbiology and Infection Control, Statens Serum Institut, Copenhagen, Denmark.

Plos One
|August 27, 2014
PubMed

Insights

Invasive pneumococcal disease (IPD) in infants under 90 days old decreased for PCV-7 serotypes after vaccine introduction. However, the overall IPD incidence in this age group remained unchanged.

Area of Science:

  • Pediatrics
  • Infectious Diseases
  • Vaccinology

Background:

  • The Danish childhood immunization program introduced the seven-valent pneumococcal conjugate vaccine (PCV-7) in 2007, later replaced by PCV-13 in 2010.
  • While PCV vaccines significantly reduced invasive pneumococcal disease (IPD) in vaccinated children, the impact on infants too young for vaccination remained less understood.

Purpose of the Study:

  • To analyze the incidence of IPD in infants younger than 90 days in Denmark from 1943 to 2013.
  • To specifically investigate the trends of IPD caused by vaccine-type (VT) pneumococci in this vulnerable population before and after PCV introduction.

Main Methods:

  • A retrospective study of all unvaccinated infants under 90 days with confirmed IPD (pneumococcus isolate from blood or cerebrospinal fluid) between 1943 and 2013.
  • Serotyping of all pneumococcal isolates using Pneumotest Latex and Quellung reaction to determine vaccine type coverage.

Main Results:

  • A total of 216 IPD cases were identified in infants under 90 days.
  • Incidence of IPD due to PCV-7 serotypes declined significantly and was not observed after 2009.
  • The overall incidence of IPD in infants under 90 days did not show a significant change throughout the study period.

Conclusions:

  • Pneumococcal conjugate vaccines have effectively reduced IPD caused by PCV-7 serotypes in Danish infants under 90 days.
  • Despite the decline in specific serotypes, the overall burden of IPD in the youngest infants has not been reduced by the current vaccination strategies.
Abstract

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