Abstract
Objectives
In 2003, British Columbia (BC) introduced a universal heptavalent pneumococcal conjugate vaccine (PCV-7) program for infants, and in 2007 revised the recommended schedule from four doses to three doses. We describe trends in the incidence of invasive pneumococcal disease (IPD) in association with these program changes.
Methods
All confirmed cases are reported to the BC Centre for Disease Control (BCCDC) using a standardized data collection process; isolates are forwarded to the BCCDC Public Health and Reference Microbiology Laboratory for serotyping and to the National Reference Laboratory for confirmation. Upon implementation of the reduced dose program in 2007, additional epidemiological data, including immunization history, were collected for children =16 years.
Results
Seven years after implementation of the program, a 78% decline in incidence of IPD among children under five has been achieved; this is largely a direct effect of the PCV-7 program. Among those >16 years of age, herd immunity is evident and decreasing trends of PCV-7 serotypes continued even after the dose reduction program was introduced. However, gains in disease reduction were offset by increases in replacement serotypes, particularly among the over-65 age group. This has resulted in no net change in adult IPD rates.
Conclusions
The implementation of the PCV-7 program has changed the epidemiology of IPD in BC through direct effects of the vaccine, herd immunity and serotype replacement. The introduction of a three-dose schedule was not associated with an excess of vaccine failures.
Keywords: Streptococcus pneumoniae, pneumococcal vaccines, population surveillance, immunization schedule
Résumé
Objectifs
En 2003, la Colombie-Britannique (C.-B.) a instauré un programme de vaccination antipneumococcique universelle des nourrissons par le vaccin conjugué heptavalent (PCV7), et en 2007, la province a réduit de quatre à trois le nombre de doses recommandées dans le calendrier de vaccination. Nous décrivons les tendances de l’incidence des maladies invasives à pneumocoque (MIP) associées à cette modification du programme.
Méthode
Tous les cas confirmés sont déclarés au BC Centre for Disease Control (BCCDC) selon un processus standardisé de collecte de données; les isolats sont transmis au laboratoire de santé publique et de référence en microbiologie du BCCDC pour sérotypie et au laboratoire de référence national pour confirmation. Lorsqu’on a instauré le programme à doses réduites en 2007, des données épidémiologiques supplémentaires, dont les antécédents vaccinaux, ont été recueillies pour les enfants de 16 ans et moins.
Résultats
Sept ans après la mise en œuvre du programme, l’incidence des MIP chez les enfants de moins de cinq ans a baissé de 78%; c’est dans une large mesure un effet direct du programme PCV7. Chez les moins de 16 ans, l’immunité collective est manifeste, et la tendance baissière des sérotypes avec le PCV7 s’est maintenue même après l’instauration du programme à doses réduites. Cependant, les gains obtenus au chapitre de la diminution de la maladie ont été compensés par la hausse des sérotypes de remplacement, particulièrement chez les plus de 65 ans. Il n’y a donc eu aucun changement net dans les taux de MIP chez les adultes.
Conclusion
La mise en œuvre du programme PCV7 a modifié de trois façons l’épidémiologie des MIP en C.-B.: par l’effet direct du vaccin, l’immunité collective et le remplacement des sérotypes. L’instauration du calendrier de vaccination en trois doses n’était pas associée à un surcroît d’échecs vaccinaux.
Mots clés: streptococcus pneumoniae, vaccins antipneumococciques, surveillance de population, calendrier vaccinal
Footnotes
Conflict of Interest: None to declare.
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