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Review 1: "Mitigating the 4th Wave of the COVID-19 Pandemic in Ontario"

Published onJul 27, 2022
Review 1: "Mitigating the 4th Wave of the COVID-19 Pandemic in Ontario"
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key-enterThis Pub is a Review of

ABSTRACTBackgroundThe 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 4th wave fueled by the Delta variant, or whether the reinstitution of more intense public health measures will be required.MethodsWe 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.ResultsMaintaining 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.DiscussionHigh 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.

RR:C19 Evidence Scale rating by reviewer:

  • Reliable. The main study claims are generally justified by its methods and data. The results and conclusions are likely to be similar to the hypothetical ideal study. There are some minor caveats or limitations, but they would/do not change the major claims of the study. The study provides sufficient strength of evidence on its own that its main claims should be considered actionable, with some room for future revision.



The forecast of COVID-19 cases and the need for hospital resources in a mid-size town in Southwestern Ontario are discussed in this study. The goal of the study is to see if ongoing vaccination and contact reduction strategies can manage the Delta variation. The study was initiated in the light of the restart of in-person K-12 and postsecondary education to assess the public health interventions. The findings reveal that, even if the current scenario persists (17 percent contact reduction compared to the previous months), hospital admissions may exceed 20 percent of the previous critical care capacity by late October. According to the findings of the study, the predicted number of pediatric critical care hospitalizations may exceed 20 percent of the capacity. The research concludes that despite the high rate of vaccination and strong mask-wearing laws, authorities should make quick additional efforts to reduce contacts (30% contact reduction compared to past situations) to avoid re-instituting strict health measures.

The proposed model is extended from the previous research of the same authors. Even though the model structure is given, the underlying mathematical model is not obvious. The method of estimation of model parameters and the reproduction number or rate is not given. To validate the results, it is recommended to provide the mathematical proof since a deterministic compartmental model is proposed in the research. In the Methods section, references to APPENDIX FIGURE (1-6) are given, but it is not found in the paper. A reference is given to Table 5 and Table 6 in the Results section, but unable to locate the referenced tables in the paper. The findings forecast the number of new infections each day, ward bed occupancy, and ICU bed occupancy at various levels of contact reduction. But the basis/proof of the projection calculation is not shown. Limitations are discussed and the recent literature is cited in the paper. The paper is concerned about the Delta variant and urge the authorities for appropriate action to decrease the contacts and to expect more cases of pediatric critical care hospitalizations as the said group is more prone to the infection because of non-vaccinated category. There are no ethical concerns. Claims are generally supported by the data and methods used. Decision-makers should consider the claims in this study actionable with limitations based on the methods and data.

The manuscript is recommended for publication with the above concerns addressed.


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