Here, we discuss our group’s most recent Ontario COVID-19 forecasts, and elaborate on a key modelling decision that enabled us to predict Ontario’s third wave accurately, weeks in advance, while infection reports were still declining.
Every two weeks, our group provides COVID-19 infection report forecasts for the province of Ontario to the Ontario Modelling Consensus Table, a partner of the Ontario Science Advisory Table, which presents this information to the Health Coordination Table of the Ontario Ministry of Health.1
Our forecasts are based on a compartmental epidemic model implemented in our publicly available
McMasterPandemic R package, and involve statistical fits to the province’s latest infection report data.
We made a forecast on 21 Feb 2021, when infection reports were still declining steadily from a peak in early January. At the time, we were asked to consider what would happen if public health measures were to relax in early March.
Our model predicted exponential growth in infection reports very soon after an early-March reduction in public health measures. This prediction was rather startling at the time, especially given that infection reports appeared to still be declining.
Public health measures did indeed relax further in early March: on March 8th, the province lifted the January stay-at-home order in the last few regions where it was still in effect (Toronto, Peel, and North Bay Parry Sound) and loosened restrictions in seven other regions.
Infection reports began growing exponentially soon after our forecast was made, propelling Ontario into its third, and largest, wave of infection as of early April 2021.
When we made a forecast on 20 Mar 2021, infection reports had been increasing for a few weeks, so we were able to calibrate the growth rate of the third wave more precisely than in the 21 Feb forecast. We presented a “status quo” forecast, where we assumed that there were no changes to public health policy after the forecast date.
Our model once again predicted exponential growth in infection reports into April 2021.