20 May 2022

Study to assess the incidence of COVID-19 in Quebec - Updated with data from the week of May 12 to 17, 2022

CIRANO has published the latest update of its exploratory study to estimate the incidence of COVID-19 cases in Quebec. This update integrates the data from the eighteenth week of collection, which took place May 12 to 17, 2022, with a sample of 3000 respondents representative of the Quebec population and compares them to other collection weeks.

It should be noted that this study was conducted over 18 consecutive weeks since January 13, 2022, in order to monitor the evolution of the situation. The study uses both a direct sampling strategy and an indirect sampling estimation based on the network scale-up (NSS) method. Details of the methods are available in the CIRANO 2022s-03 working paper.

CIRANO fulfilled its mission to support and inform public decision making by setting up this exploratory study to estimate the incidence of COVID-19 cases as early as the beginning of January at a time when Quebec was experiencing a very strong increase in cases and when access to screening by PCR tests was then limited to essential workers. In order to compensate for this lack of data, a multidisciplinary and inter-university team of researchers from CIRANO was formed and has been producing weekly analyses for the past 18 weeks that have really allowed the government to better monitor the pandemic.
The last few weeks have validated the network amplifier method: standard deviations are lower and there is more precision in the estimation of the trend of cases.
In this context, CIRANO is now transferring the entire method to the Institut national de santé publique du Québec (INSPQ) who will continue the analyses in the future.
This project is a very relevant example of CIRANO's mission, which testifies to the value of the studies carried out at CIRANO.

→ Eighteenth week of collection (May 12 to 17, 2022)

Highlights:

Decrease in the incidence of cases relative to the previous week for all estimators (significant decrease for 3 out of 4 indicators - decrease varying from 14% to 36% depending on the estimator used). Between 14,000 and 23,000 cases per day, depending on the estimation method used. Significant decline in case incidence for two age groups (40-49 and over 70) and non-significant decline for all other groups. Decrease or stability in case incidence for all regions and region groupings. These trends by region groups mask region-specific variations.
Reinfections: 33.5% of individuals infected in the week ending May 12-17, 2022 had had COVID-19 previously. For 40% of these cases, the 1st infection occurred between December 2021 and February 2022.

This study was conducted by a team of researchers composed of David Boisclair (HEC Montréal), Roxane Borgès Da Silva (Université de Montréal and CIRANO), Vincent Boucher (Université Laval) Nathalie de Marcellis-Warin (Polytechnique Montréal and CIRANO), Pierre-Carl Michaud (HEC and CIRANO), Ingrid Peignier (CIRANO) and Alexandre Pud'Homme (Université de Montréal).