A new study that looks back on the first and second waves of the pandemic in 2020 and 2021 says that travel restrictions barring entry to Canada did drastically reduce the number of COVID-19 cases entering the country.
However, researchers say, it still wasn鈥檛 enough to stop new outbreaks.
In the study, on Tuesday, researchers with the University of British Columbia looked at public data on viral genome sequences collected in 2020 and early 2021 to find the geographic source of specific chains of COVID-19 transmission.
They found that four weeks after Canada restricted entry from most foreign nationals in March 2020, the number of COVID-19 cases crossing the border into the country had dropped 10-fold.
鈥淐OVID-19 importations were accelerating in the lead up to March 2020 but experienced a sharp and drastic decline after travel restrictions were put in place,鈥 Angela McLaughlin, a PhD candidate in bioinformatics at UBC and the study鈥檚 lead author, said in a .
鈥淭he data shows that federal travel restrictions can be effective in reducing viral importations when implemented rapidly.鈥
But COVID-19 was already here, and travel restrictions couldn鈥檛 stop that.
The spring and summer of 2020 saw daily case levels at one of their lowest nationally, but circulation was still occurring within the country, the study outlined, with specific chains of transmission persisting into the fall of 2020.
As travel restrictions eased in November 2020, allowing more entrance into the country as well as shortened quarantine requirements, the international importation of COVID-19 cases rebounded.
Variants of concern, beginning with the Alpha variant, began to make their way into Canada. Researchers estimated 30 unique genetic sublineages of the Alpha variant, also known as B.1.1.7, had entered the country by the end of February 2021.
Numerous factors, such as the state of the global fight against COVID-19, including the emergence of these variants elsewhere in the world, make it harder for travel restrictions to have an impact later on in the pandemic, researchers said.
鈥淭ravel restrictions have a diminishing return if domestic transmission is high, if highly transmissible variants become widespread globally, or if there are many individuals exempt from travel restrictions and quarantine without access to rapid testing,鈥 says McLaughlin.
On March 21, 2020, in response to the pandemic, the U.S. and Canada mutually closed the border to recreational travel after having already shut its borders to most non-citizens looking to enter the country.
Within a month after these restrictions, researchers found that importations of COVID-19 declined from 58.5 sublineages of the virus on average per week to just 10.3-fold lower within four weeks.
There were still 鈥渘ewly seeded sublineages鈥 over the summer of 2020 as domestic transmission continued. Travel restrictions were relaxed slightly in the fall, although the U.S. land border did not re-open to non-essential travel until August 2021.
During the first wave of the pandemic in early 2020, 49 per cent of viral importations 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 biggest international source of COVID-19 for Canada in the second wave, according to the data, at 43 per cent. Cases from India made up 16 per cent of those that came from outside of the country in the second wave, while cases from the U.K. made up seven per cent.
If restrictions had been kept at their maximum for longer, they could鈥檝e held off more transmission, researchers posited, but this would鈥檝e come with consequences in other areas.
鈥淭he social and economic repercussions of travel restrictions must be weighed relative to the risk of unhampered viral importations, which have the potential to overburden the health-care system,鈥 Mclaughlin said.
鈥淲e are now in the era of infectious disease,鈥 Dr. Jeffrey B. Joy, an assistant professor at UBC鈥檚 department of medicine and the study鈥檚 senior author, said in the release. 鈥淭his study highlights the increasing importance of genomic epidemiology, enabled by sharing of genomic sequence data, in informing and evaluating public health policy to combat current and future viral outbreaks threatening society.鈥
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