Background: A 21-valent pneumococcal conjugate vaccine (PCV21) was recently authorized in Canada to protect adults against invasive pneumococcal disease (IPD). Objective: To assess the cost-effectiveness of PCV21 compared to current Canadian vaccination recommendations for adults of different age and risk groups. Methods: We used a static cohort model to estimate lifetime incremental cost-effectiveness ratios (ICERs), in 2023 Canadian dollars per quality-adjusted life year (QALY), discounted at 1.5%, in population cohorts aged 33 (midpoint of the 18-49 year age group), 50, and 65 years from the health system and societal perspectives. The primary analysis used 2022 serotype distributions for IPD cases. Additional analyses incorporated indirect effects from pediatric vaccination and used IPD serotype distributions from 2015-2019, to explore the impact of changes over time observed in some age groups. Results: For population groups currently recommended to receive PCV20 in Canada (65 years and older, 50-64 years with additional risk factors for IPD, or 18-49 years with immunocompromising conditions), PCV21 was cost-effective at a $50,000 per QALY threshold and dominated PCV20 in most scenarios when PCV21 serotypes were more prevalent. When PCV20 serotypes were equally or more prevalent than PCV21 serotypes, results were more sensitive to assumptions about indirect effects and serotype replacement. For groups not currently recommended a conjugate vaccine (50-64 years without additional IPD risk factors and 18-49 years with chronic medical conditions or unhoused populations), use of a higher-valency conjugate vaccine was a cost-effective intervention compared to no vaccination, with the optimal vaccine dependent on the proportion of IPD attributable to PCV20 and PCV21 serotypes in the population of interest. Results were sensitive to vaccine price in most scenarios. Interpretation: The use of PCV21 may be cost-effective in some populations, depending on the prevalence of IPD serotypes covered by PCV20 and PCV21.

The authors have declared no competing interest.

This research was supported, in part, by a Canada Research Chair in Economics of Infectious Diseases held by Beate Sander (CRC-2022-00362).

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