Post last updated: 21 Jun 2021

Context

Every three weeks, our group provides COVID-19 infection report forecasts for the province of Ontario to the Ontario Modelling Consensus Table (MCT), a partner of the Ontario Science Advisory Table (SAT), which presents this information to the Health Coordination Table of the Ontario Ministry of Health.1 Other modelling groups also provide forecasts to the MCT. After reviewing all forecasts provided, the MCT provides consensus projections to the SAT.

Our forecasts are based on a compartmental epidemic model implemented in our publicly available McMasterPandemic R package, and involve statistical fits to Ontario’s latest infection report data.

Forecast overview

The forecast presented here was made on 5 Jun 2021 and submitted to the MCT for inclusion in the public briefing by the SAT on 10 June.

This set of forecasts incorporates an enhanced two-dose vaccination model, as well as the projected replacement of the Alpha Variant of Concern (VoC), also known as B.1.1.7, by the more-transmissible Delta VoC (B.1.617.2).

We have updated, and will continue to update, this post in order to show the latest infection reports, but the forecasts themselves have not, and will not, be modified after the forecast date.

Forecast results

The following figure gives the infection report forecasts (curves), with 95% confidence intervals as bands around each forecast curve. Observed infection reports to which the model was fit are plotted with solid points, while observations after the fact are included as hollow points.

Forecast details

Interventions

We assume public health measures relax on 14 June, which (at the time the forecast was made) was the scheduled date for the province to move into stage 1 of its reopening plan (re-opening has since been moved up to 11 June). We explore 3 scenarios for the transmission rate upon reopening (due to increased contacts):

  1. x1.5 the estimated transmission rate under the stay-at-home order (a 50% increase);
  2. x1.75 (a 75% increase);
  3. x2 (a 100% increase).

We assume that the lifting of the 8 April stay-at-home order on 2 June has not had a significant effect on contacts (on 5 June it was too soon to estimate any such effect from infection report data due to the approximate 14-day reporting delay for infections).

Vaccination

For the model fitting period, we feed in the reported number of first and second doses administered each day.

In the forecast period, we explore 3 scenarios for the total number of doses administered per day:

  1. 142,000 doses/day (average rate for seven days up to and including the forecast date of 5 June);
  2. 180,000 doses/day (a 27% increase over the seven-day average);
  3. 213,000 doses/day (a 50% increase over the seven-day average).

In each scenario, the total dose administration rate remains constant throughout the forecast period.

We assume that the proportion of first doses administered follows a logistic curve starting on the forecast date, based on fitting the reported proportion of first doses starting from 1 May: