But, researchers say, it wasn’t enough to stop new cases. In the study, published in the journal eLife on Tuesday, researchers from the University of British Columbia examined public data on viral genome sequences collected in 2020 and early 2021 to find the geographic source of specific chains of transmission of COVID-19. They found that four weeks after Canada restricted entry by most foreign nationals in March 2020, the number of COVID-19 cases crossing the border into the country had dropped 10-fold. “Imports of COVID-19 were accelerating until March 2020, but experienced a sharp and drastic decline after travel restrictions were imposed,” Angela McLaughlin, a bioinformatics PhD candidate at UBC and lead author of the study, said in a press release. release. “The data show that federal travel restrictions can be effective in reducing virus imports when implemented quickly.” But COVID-19 was already here and travel restrictions couldn’t stop that. The spring and summer of 2020 saw daily levels of cases among the lowest nationally, but circulation still occurred within the country, the study outlined, with specific chains of transmission remaining through fall 2020. As travel restrictions eased in November 2020, allowing more entry into the country as well as shortening quarantine requirements, international importation of COVID-19 cases rebounded. Variants of concern, starting with the Alpha variant, began to enter Canada. The researchers estimated that 30 unique genetic sublines of the Alpha variant, also known as B.1.1.7, had entered the country by the end of February 2021. Many factors, such as the state of the global fight against COVID-19, including the emergence of these variants in other parts of the world, make it harder for travel restrictions to have an impact later in the pandemic, the researchers said. “Travel restrictions have diminishing returns if domestic transmission is high, if highly transmissible variants become widespread globally, or if there are many people exempt from travel restrictions and quarantine without access to rapid testing,” says McLaughlin. On March 21, 2020, in response to the pandemic, the US and Canada mutually closed their borders to leisure travel after already closing their borders to most non-citizens wishing to enter the country. Within a month of these restrictions, the researchers found that introductions of COVID-19 dropped from an average of 58.5 sublines of the virus per week to just 10.3 times lower within four weeks. There were still “new sublines” in the summer of 2020 as domestic transmission continued. Travel restrictions eased slightly in the fall, although US land borders did not reopen to non-essential travel until August 2021. During the first wave of the pandemic in early 2020, 49 percent of the viral importation of COVID-19 into Canada likely came from the U.S., the study found, entering mainly through Quebec and Ontario. The US remained the largest international source of COVID-19 for Canada in the second wave, the data showed, at 43 per cent. Cases from India made up 16 percent of those coming from abroad in the second wave, while cases from the United Kingdom made up 7 percent. If the restrictions had been kept at their maximum for longer, they could have stopped more transmission, the researchers argued, but that would have had consequences in other areas. “The social and economic impacts of travel restrictions must be weighed against the risk of unfettered virus introduction, which has the potential to overburden the health care system,” McLaughlin said. “We are now in the era of infectious diseases,” Dr. Jeffrey B. Joy, assistant professor in the UBC department of medicine and senior author of the study, said in the release. “This study highlights the growing importance of genomic epidemiology, provided by the sharing of genomic sequence data, to inform and evaluate public health policy to combat current and future viral outbreaks that threaten society.”
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