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Since Canada introduced international travel restrictions during the first wave of the Covid-19 pandemic, the number of cases entering the country has dropped tenfold.
Although the acute reduction does not translate into fewer cases, because the reduction is not enough to prevent new outbreaks, researchers say this information is important for understanding the evolution of the virus and the impact of travel restrictions.
The findings, published on August 2 eLifeGenomic data was used to estimate the geographic origin of viruses.
Angela McLaughlin
Canada’s first case of Covid-19 was discovered on January 25, 2020 in a traveler who arrived in Toronto from Wuhan, China. On March 5, the first community transmission case was identified, write Angela McLaughlin, PhD candidate in bioinformatics at the University of British Columbia, and colleagues.
Canadian authorities have issued travel restrictions to prevent foreign nationals from rushing in. On March 14, the Canadian government issued a travel advisory to avoid all non-essential travel outside the country. Two days later, all non-Canadians or non-permanent residents were banned from entering the country.
How successful were these measures?
To achieve this, McLaughlin and her team accessed publicly available viral genome sequences to create a detailed timeline of how the virus entered Canada from January 2020 to March 2021, as well as the chains of transmission that occurred.
“It highlights the importance of genomic epidemiology to identify the origin and spread of SARS-CoV-2 lineages to help guide responses to the COVID-19 pandemic,” the authors wrote.
The genomic data was used to estimate the geographic origin of the viruses. In total, the researchers identified 2263 cases of Covid-19 entering the country.
In the first wave, 49% of cases came from the US. They were introduced mainly to the provinces of Quebec (39%) and Ontario (36%).
In the second wave, the US became the main source; 43% of cases came from that country, although India contributed 16% and the UK contributed 7%.
Travel restrictions have limited new cases from entering Canada, the researchers found.
In the year In March 2020, 4 weeks after the introduction of foreign entry restrictions, the number of COVID-19 cases entering Canada dropped tenfold, from 59 cases per week to 10 cases per week.
Although this has been dramatically reduced, variants of Covid-19 have emerged and contributed to the persistence of problems in the second wave.
In November 2020, additional cases were introduced in connection with the easing of special conditions of entry for foreign nationals, the shortening of quarantine and the introduction of new emergency situations and exceptions of interest.
“If domestic transmission is high, if highly transmissible variants are prevalent globally, or if many individuals are exempt from travel restrictions and are exempt from rapid testing, travel restrictions may be eased,” McLaughlin said in a statement.
By the end of February 2021, an estimated 30 unique lineages of alpha diversity (B.1.1.7) had been introduced into Canada. That difference is increasing, displacing the original SARS-CoV-2 virus in the second half of the second wave and into the third wave.
To fully limit the number of COVID-19 cases in Canada, travel restrictions and quarantine periods would have to be permanent, the authors note.
“This study provides important observations about the distribution of SARS-CoV-2 lineages in Canada and the introduction of lineages into Canada during the first year of the COVID-19 pandemic,” he wrote. eLife Review Editor Sarah E. Kobey, PhD, University of Chicago, Chicago, Illinois.
“This information is critical to understanding SARS-CoV-2 evolution and epidemiology, including the potential impact of travel restrictions,” Cobey concluded.
The Canadian Covid-19 Genomics Network Consortium and the Canadian Public Health Laboratory Network provided access to the data used in the study. McLaughlen was supported by a Canada Health Research Doctoral Grant and a Natural Sciences and Engineering Research Council of Canada Create Scholarship.
eLife Published online August 2, 2022. Full text
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