Canada's border closures may have stemmed COVID-19 variant importsDynamic restrictions on nonessential foreign travel into Canada helped slow COVID-19 variant introductions in early 2020 and 2021, allowing the government more time to scale up vaccination, testing, and contact tracing programs, according to a study published yesterday in eLife.A team led by University of British Columbia researchers genetically sequenced SARS-CoV-2 samples in the first and second pandemic waves to estimate variants' geographic origins.
They identified 2,263 introductions of SARS-CoV-2 variants into Canada, including 680 that went on to circulate within the country and 1,582 that didn't appear to circulate.In the first wave, 49% of the sublineages originated in the United States and were introduced mainly into Quebec (39%) and Ontario (36%).
While the United States was still the predominant source of variants in the second wave (43%), India and the United Kingdom made up 16% and 7% of introductions, respectively.After Canada closed its borders to foreign travel on Apr 22, 2020, viral importations, which had peaked at 58.5 sublineages a week, fell 3.4-fold within 2 weeks and 10.3-fold within 4 weeks.
New variants, however, continued to be introduced at a low rate until the second wave began in August 2020, possibly fueled by essential foreign workers supporting the supply chain.In October 2020, after travel restrictions were eased slightly, SARS-CoV-2 introductions increased, and by the end of February 2021, an estimated 30 B.1.1.7 sublineages had been introduced.Senior author Jeffrey Joy, PhD, of the University of British Columbia, said in an eLife news release that broad and long-term restrictions against nonessential international travel