Invasive Pneumococcal Disease Epidemiology and Serotype Replacement After the Introduction of the 13-Valent Pneumococcal Conjugate Vaccine in Ontario, Canada, 2007-2022

Abstract

Background: New vaccine products were recently authorized for protection against invasive pneumococcal disease (IPD) in Canada. Our aim was to determine age- and serotype-specific trends in IPD incidence and severity in Canada's largest province, Ontario.

Methods: We included all confirmed IPD cases reported in Ontario and defined the pre-pneumococcal 13-valent conjugate vaccine (PCV13) era (01/2007 to 12/2010), post-PCV13 era (01/2011 to 12/2019), and coronavirus disease 2019 (COVID-19) pandemic era (01/2020 to 12/2022). We estimated incidence, hospitalization, and case fatality rate (CFR) by age. We grouped IPD cases by vaccine-specific serotypes (PCV13; PCV15-non-PCV13; PCV20-non-PCV13; PCV20-non-PCV15; polysaccharide 23-valent vaccine-non-PCV20; and non-vaccine-preventable [NVP]). We then compared incidence rates by age and serotype group in the pre- and post-PCV13 eras by calculating rate ratios (RRs) and their 95% CIs.

Results: Incidence and hospitalizations declined from the pre- to post-PCV13 era in children aged <5 years (RR, 0.7; 95% CI, 0.6-0.8; and RR, 0.8; 95% CI, 0.7-0.9, respectively), but the CFR increased (1.4% to 2.3%). Other age groups saw smaller declines or more stable incidence rates across the years; hospitalizations increased in adults aged 50-64 years (RR, 1.2; 95% CI, 1.1-1.4) and ≥65 years (RR, 1.1; 95% CI, 1.0-1.1). For all ages, IPD cases and hospitalizations attributable to PCV13 serotypes declined, and those attributable to PCV15-non-PCV13, PCV20-non-PCV13, and NVP serotypes increased. IPD incidence declined during the COVID-19 era.

Conclusions: IPD incidence and hospitalizations due to PCV13 serotypes decreased after PCV13 introduction but increased for other serotypes. Continued surveillance is required to evaluate changes to pneumococcal vaccination programs and ongoing changes to the distribution of IPD-causing serotypes.

Keywords: Invasive pneumococcal disease; epidemiology; serotype replacement; vaccination program.

Figure 1.

Incidence (A) and hospitalization rates (B) (per 100 000 population) of invasive pneumococcal disease cases, by age group and year, in Ontario, Canada, 2007–2022.

Figure 2.

IPD incidence, hospitalization, RRs, and 95% CIs for RR comparing the pre- and post-PCV13 periods, by age and vaccine-specific and NPV serotype groupings (A: aged <5 y; B: aged 5–49 y; C: aged 50–64 y; D: aged 65+ y). PCV13 (1, 3, 4, 5, 6A, 6B, 7F, 9V, 14, 18C, 19A, 19F, and 23F), PCV15-non-PCV13 (22F and 33F), PCV20-non-PCV13 (includes serotypes in PCV15; 22F, 33F, 8, 10A, 11A, 12F, 15B), PCV20-non-PCV15 (8, 10A, 11A, 12F, 15B), and PPV23-non-PCV20 (2, 9N, 17F, and 20) and NVP (serotypes not protected against by any of the authorized vaccines). Abbreviations: IPD, invasive pneumococcal disease; NPV, non-vaccine-preventable; PCV, pneumococcal conjugate vaccine; PPV, polysaccharide vaccine; RR, rate ratio.