Changing Epidemiology of Invasive Pneumococcal Disease in Canada, 1998-2007: Update from the Calgary-Area Streptococcus pneumoniae Research (CASPER) Study

Background. Routine infant vaccination with 7-valent pneumococcal conjugate vaccine (PCV7) began in the Calgary Health Region (Alberta, Canada) in 2002. We measured the impact of this vaccine program on invasive pneumococcal disease (IPD). Methods. Prospective, population-based surveillance of all cases of IPD (with culture specimens obtained from sterile sites) was conducted from January 1998 through December 2007. Demographic and clinical data were collected. All viable isolates were saved and serotyped. Results. There were 1182 IPD cases over the 10-year period. Comparison of the vaccine period (2003-2007) with the prevaccine period (1998-2001) revealed that the incidence of IPD due to PCV7 serotypes decreased significantly by 86%, 59%, 38%, and 78% in the 6-23-month, 2-4-year, 16-64-year, and 65-84-year age groups, respectively. The total number of IPD cases decreased by 77%, 45%, and 34% in the 6-23-month, 2-4-year, and 65-84-year age groups, respectively. The incidence of IPD due to non-PCV7 serotypes increased by 183%, and the total incidence of IPD increased by 73% among adults aged 16-64 years; however, this increase was primarily attributed to a large outbreak of serotype 5 IPD among homeless adults during the period 2005-2007. There were 5 cases of IPD due to PCV7 serotypes among vaccinated children in the vaccine period. Conclusions. Since the introduction of PCV7 vaccine, there has been a profound decrease in the total number of cases of IPD among children and in cases due to PCV7 serotypes among subjects of all ages in Calgary, indicating a strong direct effect and herd effect of the vaccine. The serotypes that now cause IPD have changed significantly. The magnitude and impact of replacement IPD caused by non-PCV7 serotypes is not yet known.