Travel restrictions have significantly reduced the number of COVID-19 cases entering Canada – but not enough to prevent new outbreaks

Science, Health & Technology

08/02/2022 | Contact for more information Brett Goldhawk

Canada’s restrictions on international travel have drastically reduced the number of COVID-19 cases entering the country during the first waves of the pandemic, but weren’t enough to prevent new outbreaks, according to a new study led by researchers from the University of British Columbia.

The study published today in eLife, used publicly available viral genome sequences to create a detailed timeline of how the virus got to Canada from January 2020 to March 2021, and the resulting chains of transmission. The genomic data was used to identify the geographic origin of COVID-19 cases, which enabled the identification of 2,263 cases where COVID-19 was imported into the country. It is the first national-level genomic analysis of the COVID-19 epidemiology in Canada.

The findings shed new light on the effectiveness of Canada’s border measures, showing that the number of COVID-19 cases entering Canada has fallen four weeks after restrictions were imposed in March 2020, banning entry for most foreigners has decreased tenfold.

“COVID-19 imports accelerated leading up to March 2020, but experienced a sharp and drastic drop after travel restrictions were put in place,” says Angela McLaughlin (she/her), a PhD student in bioinformatics at UBC and lead author of the study. “The data shows that federal travel restrictions can be effective in reducing viral imports if implemented quickly.”

Although travel restrictions significantly reduced COVID-19 imports, they were not eliminated and continued at a lower level into spring and summer 2020. This led to new chains of transmission that greatly contributed to the persistence of COVID-19 cases in the aftermath of the second wave. Imports continued to recover in November 2020 as entry exemptions for foreigners were eased and quarantine shortened, bringing emerging variants of concern (VOCs) and interests (VOIs).

“Travel restrictions have diminishing benefits when domestic transmission is high, when highly transmissible variants are spreading globally, or when many people without access to rapid testing are exempt from travel restrictions and quarantine,” says McLaughlin.

By the end of February 2021, an estimated 30 unique alpha variant (B.1.1.7) genetic sublineages had been imported into Canada, progressively supplanting the original SARS-CoV-2 virus through the second half of the second wave and into the third wave.

The researchers say travel restrictions and quarantine periods would need to be maintained to fully reduce Canada’s COVID-19 burden, but ultimately these restrictions come with a trade-off.

“The social and economic impact of travel restrictions must be weighed against the risk of unchecked virus entry, which can potentially overwhelm the healthcare system,” says Mclaughlin.

Of virus imports during the first wave of COVID-19, data suggests that 49 percent likely originated in the US, with imports mostly in Quebec and Ontario. In the second wave of COVID-19, the US was still the dominant source of virus entry at 43 percent, alongside larger contributions from India at 16 percent and the UK at seven percent.

The study was led by researchers from UBC and the BC Center for Excellence in HIV/AIDS (BC-CfE) along with colleagues from Western University, the University of Arizona and the Canadian COVID-19 Genomics Network (CanCOGeN). The researchers say the study provides important insights into the effectiveness of public health interventions that will help shape how we respond to future viral threats.

“We are now in the age of infectious diseases,” says the study’s lead author, Dr. Jeffrey B Joy (he him), Assistant Professor at UBC School of Medicine and Principal Investigator at BC-CfE. “This study highlights the increasing importance of genomic epidemiology, enabled by the sharing of genome sequence data, to inform and assess public health policies to combat current and future viral outbreaks that threaten society.”

Interview language(s): English