Invasive Pneumococcal Disease Epidemiology and Conjugate Vaccines in Canada, 2000-2019

Area of Science:

• Infectious Diseases
• Vaccinology
• Epidemiology

Background:

• Invasive pneumococcal disease (IPD) remains a significant global health concern.
• Pneumococcal conjugate vaccines (PCVs) have been implemented in childhood immunization programs to reduce IPD incidence.
• Despite vaccination efforts, IPD continues to pose a burden, necessitating ongoing epidemiological surveillance and vaccine strategy evaluation.

Purpose of the Study:

• To analyze the epidemiology of IPD in Canada following the introduction of 7-valent (PCV7) and 13-valent (PCV13) pneumococcal conjugate vaccines.
• To evaluate the potential impact of newer vaccines, including PCV15, PCV20, and PCV21, on IPD serotype distribution.
• To assess the effectiveness of PCV7 and PCV13 in reducing IPD rates across different age groups and identify trends in vaccine-emergent serotypes.

Main Methods:

• A cross-sectional study analyzing 37,921 IPD isolates from Canada between 2000 and 2019.
• Incidence rates and proportion analyses were conducted for serotypes covered by PCV7, PCV13, PCV15, PCV20, and PCV21.
• Generalized linear piecewise quasi-Poisson regression models were used to assess the impact of PCV7 and PCV13 introduction on IPD rates.

Main Results:

• PCV7 introduction led to significant reductions in PCV7-specific serotype IPD rates (98.5% in children <5 years).
• PCV13 introduction also decreased PCV13-only serotype IPD rates (90.6% in direct cohort, 57.1% in indirect cohort).
• Despite reductions, IPD increased due to emerging non-vaccine types and persistence of serotypes 3, 4, and 19F, particularly in adults. Potential serotype coverage by PCV15, PCV20, and PCV21 ranged from 23% to 49%, with non-vaccine types comprising 45-52%.

Conclusions:

• Initial reductions in IPD following PCV introduction were observed, but overall IPD rates in Canada increased.
• Indirect protection from PCVs was limited, especially in older adults, indicating a need for direct adult vaccination strategies.
• While PCV15, PCV20, and PCV21 may enhance serotype coverage, continued development of broader-spectrum vaccines is crucial for further reducing the IPD burden.