A new study looking at the first and second waves of the pandemic in 2020 and 2021 says travel restrictions banning entry to Canada have dramatically reduced the number of COVID-19 cases entering the country.
However, researchers say this is still not enough to stop new outbreaks.
In the study, published in the peer-reviewed journal eLife on Tuesday, University of British Columbia researchers looked at public viral genome sequence data collected in 2020 and early 2021 to find the geographic source of specific chains of COVID transmission -19.
They found that four weeks after Canada restricted entry to most foreign nationals in March 2020, the number of COVID-19 cases crossing the border into the country dropped 10-fold.
“The importation of COVID-19 accelerated until March 2020, but experienced a sharp and drastic decline after travel restrictions were put in place,” Angela McLaughlin, a PhD student in bioinformatics at UBC and lead author of the study, said in a press release.
“Evidence shows that federal travel restrictions can be effective in reducing virus importation when implemented quickly.”
But COVID-19 was already here and travel restrictions couldn’t stop that.
In the spring and summer of 2020, daily case rates were among their lowest nationally, but transmission was still occurring across the country, the study said, with specific chains of transmission continuing into fall 2020.
As travel restrictions were eased in November 2020, allowing more entries into the country as well as reduced quarantine requirements, international importation of COVID-19 cases has rebounded.
Variants of concern, starting with the Alpha variant, have begun to make their way into Canada. Researchers estimate 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.
Multiple factors, such as the state of the global fight against COVID-19, including the emergence of these variants elsewhere in the world, make it difficult for travel restrictions to have an impact later in the pandemic, researchers said.
“Travel restrictions have diminishing returns if internal transmission is high, if highly portable 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 the border to recreational travel, after having already closed their borders to most non-citizens seeking to enter the country.
Within a month of these restrictions, the researchers found that importation of COVID-19 dropped from an average of 58.5 sublines of the virus per week to just 10.3 times less within four weeks.
There were still “newly laid sublines” in the summer of 2020 as internal transmission continued. Travel restrictions were eased slightly in the fall, although the US land border 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 primarily through Quebec and Ontario.
The U.S. was still the largest international source of COVID-19 for Canada in the second wave, according to the data, at 43 percent. Cases from India made up 16 percent of those who came from outside the country in the second wave, while cases from the United Kingdom made up seven percent.
If the restrictions were kept at their maximum for longer, they could have stopped more transmission, the researchers said, but that would have had consequences in other areas.
“The social and economic consequences of travel restrictions must be weighed against the risk of unfettered importation of viruses that have the potential to overburden the health care system,” McLaughlin said.
“We are now in the era of infectious diseases,” Dr. Jeffrey B. Joy, an 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, enabled by sharing genome sequence data, in informing and evaluating public health policy to combat current and future viral outbreaks threatening society.”
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