A methodology for estimating SARS-CoV-2 importation risk by air travel into Canada between July and November 2021

Milwid, Rachael M.; Ogden, Nicholas H.; Turgeon, Patricia; Fazil, Aamir; London, David; de Montigny, Simon; Rees, Erin E.

A methodology for estimating SARS-CoV-2 importation risk by air travel into Canada between July and November 2021

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dc.contributor.author: Milwid, Rachael M.; Ogden, Nicholas H.; Turgeon, Patricia; Fazil, Aamir; London, David; de Montigny, Simon; Rees, Erin E.; Rees, Erin E.
dc.date.accessioned: 2024-11-08T20:03:03Z
dc.date.available: 2024-11-08T20:03:03Z
dc.date.issued: 2024-04-19
dc.description - en: The speed and range with which COVID-19 spread globally can largely be attributed to global interconnectedness through air travel. Governments, including the Government of Canada, implemented border measures such as pre-departure screening in an attempt at preventing the importation of COVID-19. It is important to evaluate the intervention strategies to identify their impact, as well as areas for improvement. A mathematical model was developed to assess the global importation risk of COVID-19 cases into Canada, at both the national and airport levels. The model was further used to simulate counterfactual scenarios in which testing was not required for fully vaccinated (scenario 1) or any (scenario 2) travelers entering Canada for non-essential reasons. By using empirical travel volume, vaccination, and infection data, we demonstrate the utility and flexibility of the model at characterizing the importation risk, as well as showing that pre-departure testing was highly impactful in the prevention of COVID-19 importations in the Canadian context.
dc.description.abstract - en: BACKGROUND: Estimating rates of disease importation by travellers is a key activity to assess both the risk to a country from an infectious disease emerging elsewhere in the world and the effectiveness of border measures. We describe a model used to estimate the number of travellers infected with SARS-CoV-2 into Canadian airports in 2021, and assess the impact of pre-departure testing requirements on importation risk. METHODS: A mathematical model estimated the number of essential and non-essential air travellers infected with SARS-CoV-2, with the latter requiring a negative pre-departure test result. The number of travellers arriving infected (i.e. imported cases) depended on air travel volumes, SARS-CoV-2 exposure risk in the departure country, prior infection or vaccine acquired immunity, and, for non-essential travellers, screening from pre-departure molecular testing. Importation risk was estimated weekly from July to November 2021 as the number of imported cases and percent positivity (PP; i.e. imported cases normalised by travel volume). The impact of pre-departure testing was assessed by comparing three scenarios: baseline (pre-departure testing of all non-essential travellers; most probable importation risk given the pre-departure testing requirements), counterfactual scenario 1 (no pre-departure testing of fully vaccinated non-essential travellers), and counterfactual scenario 2 (no pre-departure testing of non-essential travellers). RESULTS: In the baseline scenario, weekly imported cases and PP varied over time, ranging from 145 to 539 cases and 0.15 to 0.28%, respectively. Most cases arrived from the USA, Mexico, the United Kingdom, and France. While modelling suggested that essential travellers had a higher weekly PP (0.37 – 0.65%) than non-essential travellers (0.12 – 0.24%), they contributed fewer weekly cases (62 – 154) than non-essential travellers (84 – 398 per week) given their lower travel volume. Pre-departure testing was estimated to reduce imported cases by one third (counterfactual scenario 1) to one half (counterfactual scenario 2). CONCLUSIONS: The model results highlighted the weekly variation in importation by traveller group (e.g., reason for travel and country of departure) and enabled a framework for measuring the impact of pre-departure testing requirements. Quantifying the contributors of importation risk through mathematical simulation can support the design of appropriate public health policy on border measures.
dc.identifier.doi: https://doi.org/10.1186/s12889-024-18563-1
dc.identifier.issn: 1471-2458
dc.identifier.pubmedID: 38641571
dc.identifier.uri: https://open-science.canada.ca/handle/123456789/3121
dc.language.iso: en
dc.publisher - en: BioMed Central Ltd
dc.publisher - fr: BioMed Central Ltd
dc.rights - en: Creative Commons Attribution 4.0 International (CC BY 4.0)
dc.rights - fr: Creative Commons Attribution 4.0 International (CC BY 4.0)
dc.rights.uri - en: https://creativecommons.org/licenses/by/4.0/
dc.rights.uri - fr: https://creativecommons.org/licenses/by/4.0/deed.fr
dc.subject - en: Health; Coronavirus diseases; Travel
dc.subject - fr: Santé; Maladie à coronavirus; Voyage
dc.subject.en - en: Health; Coronavirus diseases; Travel
dc.subject.fr - fr: Santé; Maladie à coronavirus; Voyage
dc.title - en: A methodology for estimating SARS-CoV-2 importation risk by air travel into Canada between July and November 2021
dc.type - en: Article
dc.type - fr: Article
local.acceptedmanuscript.articlenum: 1088
local.article.journaltitle - en: BMC Public Health
local.article.journalvolume: 24
local.pagination: 1-13
local.peerreview - en: Yes
local.peerreview - fr: Oui