Forecasting the Burden of Invasive Pneumococcal Disease in Post-Pandemic Ontario, Canada

Background

Infectious disease incidence declined during the COVID-19 pandemic; however, a resurgence has been reported in the post-pandemic period following the relaxation of COVID-19 control measures. Forecasting uses surveillance data to predict infectious disease burden and inform public health response. This study used forecasting to assess the burden of invasive pneumococcal disease (IPD), in Ontario, Canada.

Methods

Monthly IPD incidence and quarterly population data, between January 2011 - December 2024, were collected through the integrated Public Health Information System (iPHIS) and Statistics Canada, respectively. A generalized linear autoregressive moving average (GLARMA) model fit with pre-pandemic data and an interrupted time series GLARMA model fit with complete (i.e., pre-pandemic, pandemic, and post-pandemic) data, were used to forecast the mean annual IPD incidence rates for 2025-2026.

Results

During the pre-pandemic period (January 2011 – February 2020), IPD incidence remained stable (IRR = 1.01, 95% CI: 0.99-1.03). In contrast, during the post-pandemic period (May 2022 – December 2024), there was a significant increase in IPD incidence (IRR = 1.21, 95% CI: 1.12-1.31). Using the model fit with pre-pandemic data, a mean annual IPD rate of 8.41 cases per 100,000 was projected for 2025-2026. However, the model capturing all data projected a mean annual IPD rate of 16.0 cases per 100,000. Based on the most recent provincial surveillance data, a mean annual IPD rate of 11.7 cases per 100,000 was observed in 2025.

Conclusions

IPD incidence rates in Ontario, Canada increased during the post-pandemic period. The projected increase in IPD incidence rates between 2025-2026, consistent with the observed increase in 2025, indicates the persistent burden of IPD. This highlights the need for enhanced surveillance to better understand and respond to the changing dynamics of IPD.

Key messages

• IPD incidence has increased after the COVID-19 pandemic and may continue to increase in the future.

• Enhanced surveillance is essential to understand and effectively respond to the changing dynamics of IPD.