Importation of SARS-CoV-2 following the“semaine de relâche”and Québec’s COVID-19 burden - a mathematical modeling study

Abstract

Background: The Canadian epidemics of COVID-19 exhibit distinct early trajectories, with Québec bearing a very high initial burden. The semaine de relâche, or March break, took place two weeks earlier in Québec as compared to the rest of Canada. This event may have played a role in the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We aimed to examine the role of case importation in the early transmission dynamics of SARS-CoV-2 in Québec. Methods: Using detailed surveillance data, we developed and calibrated a deterministic SEIR-type compartmental model of SARS-CoV-2 transmission. We explored the impact of altering the number of imported cases on hospitalizations. Specifically, we investigated scenarios without case importation after March break, and as scenarios where cases were imported with the same frequency/timing as neighboring Ontario. Results: A total of 1,544 and 1,150 returning travelers were laboratory-confirmed in Québec and Ontario, respectively (with symptoms onset before 2020-03-25). The cumulative number of hospitalizations could have been reduced by 55% (95% credible interval [95%CrI]: 51-59%) had no cases been imported after Québec's March break. However, had Québec experienced Ontario's number of imported cases, cumulative hospitalizations would have only been reduced by 12% (95%CrI: 8-16%). Interpretation: Our results suggest that case importation played an important role in the early spread of COVID-19 in Québec. Yet, heavy importation of SARS-CoV-2 in early March could be insufficient to resolve interprovincial heterogeneities in cumulative hospitalizations. The importance of other factors -public health preparedness, responses, and capacity- should be investigated.

Is SARS-CoV-2 elimination or mitigation best? Regional and disease characteristics determine the recommended strategy

“…Previous studies considering the impact of travel measures to reduce the risk of SARS-CoV-2 importation have been controversial [16], and the implementation of withinstate travel restrictions have been subject to legal challenges [98]. While some studies have questioned the effectiveness of travel measures [7,24,105], others have emphasized their importance [32,46]. We suggest this disagreement may be due to overlooking the regional context: for example, whether community spread is occurring (Box 1), and low health care capacity, characteristics of small jurisdictions that may make elimination feasible, and the relatively low cost of implementing travel restrictions as compared to treating infections in a small economy (Fig.…”

“…In these cases, a disease mitigation approach consisting of moderate community NPIs may be sufficient to ensure hospital capacity limits are not exceeded, and strict travel measures may lead to unnecessary costs and disruptions, that could negatively affect the compliance with other public health measures [115,30]. Even when health care capacity is high, concerns regarding pathogen variants that are highly transmissible or virulent, and uncertainty in how cases will respond to interventions may justify the precautionary implementation of an elimination approach (or a 'wait-and-see approach' [78]) rather than a mitigation approach, in order to delay pathogen spread until more information is available, vaccines or therapy is developed, or response preparedness is enhanced [46,32,1,6].…”

Is the Unequal COVID–19 Burden in Canada Due to Unequal Levels of Citizen Discipline across Provinces?

“…Given the seemingly consensual nature of government officials’ initial responses to the pandemic, it is rather puzzling that Canadian provinces followed such different trajectories in terms of public health outcomes. A number of explanations have been offered to explain these outcomes, including the timing of the March school break in Quebec, which has been shown to have played a limited role ( Godin et al 2020 ). Given the similarities in the measures that different provincial governments took to limit the spread of the COVID-19 virus, another explanation—echoed by Quebec health minister Dubé—is that regional and cultural differences in compliance with governments’ preventive measures are key to explaining the heterogeneity in health outcomes.…”

Quarantine and the risk of COVID-19 importation

“…Previous studies [7][8][9][10][11][12][13][14][15][16] have considered the link between transportation and importation of COVID-19. We complement these studies here by finely decomposing the process through which cases are imported into different types of events and focusing on the role of the rate at which a location is 'challenged' by importations.…”