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The goal of this study was to project the number of COVID-19 cases and demand for acute hospital resources for Fall of 2021 in a representative mid-sized community in southwestern Ontario. We sought to evaluate whether current levels of vaccine coverage and contact reduction could mitigate a potential 4 th wave fueled by the Delta variant, or whether the reinstitution of more intense public health measures will be required.


We developed an age-stratified dynamic transmission model of COVID-19 in a mid-sized city (population 500,000) currently experiencing a relatively low, but increasing, infection rate in Step 3 of Ontario’s Wave 3 recovery. We parameterized the model using the medical literature, grey literature, and government reports. We estimated the current level of contact reduction by model calibration to cases and hospitalizations. We projected the number of infections, number of hospitalizations, and the time to re-instate high intensity public health measures over the fall of 2021 under different levels of vaccine coverage and contact reduction.


Maintaining contact reductions at the current level, estimated to be a 17% reduction compared to pre-pandemic contact levels, results in COVID-related admissions exceeding 20% of pre-pandemic critical care capacity by late October, leading to cancellation of elective surgeries and other non-COVID health services. At high levels of vaccination and relatively high levels of mask wearing, a moderate additional effort to reduce contacts (30% reduction compared to pre-pandemic contact levels), is necessary to avoid re-instating intensive public health measures. Compared to prior waves, the age distribution of both cases and hospitalizations shifts younger and the estimated number of pediatric critical care hospitalizations may substantially exceed 20% of capacity.


High rates of vaccination coverage in people over the age of 12 and mask wearing in public settings will not be sufficient to prevent an overwhelming resurgence of COVID-19 in the Fall of 2021. Our analysis indicates that immediate moderate public health measures can prevent the necessity for more intense and disruptive measures later.

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  1. SciScore for 10.1101/2021.09.02.21263000: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    NIH rigor criteria are not applicable to paper type.

    Table 2: Resources

    No key resources detected.

    Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    Our study has several limitations. First, in the Canadian healthcare system, no region is entirely self-contained. During wave 3, patients were transferred for ICU and hospital care between cities, regions, and provinces. In addition, pediatric hospital resources are organized differently from adult resources, the catchment area for the former being approximately three times the size of the latter. Second, our triggers for behaviour and policy change were set around total critical care occupancy, driven largely by adult use; at a 30% contact reduction, peak pediatric ICU demand was 0.07 per 100,000 population (representing 1.4 pediatric ICU beds adjusting for the catchment population of 2 million for the pediatric hospital), which still exceeds 10% of capacity. Higher rates of infection in children may lead to more rapid adoption of behaviour change, but the lower relative capacity in pediatric critical care will require policy makers to respond to rates of utilization in pediatric facilities specifically. Third, our model does not incorporate waning vaccine efficacy. While 65% of the vaccinated population was vaccinated after April 1 (within the past 4 months), our model may underestimate infection risk and disease severity in the older adult population because 75% of people over the age of 70 years and almost all long-term care residents were vaccinated more than 4 months ago [2, 3]. Finally, we do not consider seasonality or a transition towards indoor contacts as the weat...

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: We did not find any issues relating to colormaps.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • No protocol registration statement was detected.

    Results from scite Reference Check: We found no unreliable references.

    About SciScore

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