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Travel Strictures in Canada Slowed SARS-Cov-2 Variant Arrivals-Briefly
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30th CROI, Conference on Retroviruses and Opportunistic Infections, February 19-22, 2023, Seattle
Mark Mascolini
Flight bans and tightened passenger screening proved effective in slowing imports of new SARS-CoV-2 variants into Canada, according to phylogenetic analyses by researchers from the British Columbia Centre for Excellence in HIV/AIDS [1]. But benefits of such measures typically lasted only briefly as the targeted variant spread globally and started seeping into Canada via other routes.
Few COVID prevention tactics met more doubt than air travel bans and passenger screenings aimed at shutting off the flow of new SARS-CoV-2 variants thought to spring from a circumscribed region. Canada seemed as assiduous as any country in deploying such cordons against each new variant wave, with measures taken to ban Alpha, Beta, Gamma, Delta, and Omicron variants.
To learn whether travel restrictions limited variant importation, and for how long, Angela McLaughlin and Jeffrey Joy from the University of British Columbia used phylogenetic analysis to trace the arrival and spread of SARS-CoV-2 sublineages. Reviewing earlier national attempts to block entry of SARS-CoV-2 in its evolving guises, McLaughlin and Joy found mixed evidence that these strategies work-or that they have a lasting effect. Travel restrictions like banning flights from certain countries, quarantining international travelers, and screening arrivals at borders banned the coronavirus briefly, incompletely, or not at all.
Canada jumped into the travel restriction business in March 2020, when the country tried to slam the door on SARS-CoV-2 by banning entry of all foreign nationals. Within 4 weeks, the country saw a 10-fold drop in viral sublineages per week, but a second wave of "newly seeded sublineages" wiped out those gains. The March 2020 restrictions "did not eliminate SARS-CoV-2 introductions into Canada," McLaughlin and Joy confirmed.
As the pandemic rolled on, Canada tried different tactics against major variants clearing customs at overseas airports:
Alpha: Temporary suspension of flights from United Kingdom
Beta: Enhanced screening for people who had traveled to South Africa
Gamma: Enhanced screening and quarantine measures for people who had traveled to Brazil
Delta: Temporary suspension of flights from India
Omicron: Enhanced screening and quarantine for Canadians and banned entry of foreign nationals who had traveled to southern Africa
Alpha-blocking measures, the researchers found, yielded a "modest reduction of [the] importation rate and subsequent rebound." Anti-Delta schemes led to a "drastic reduction" in Delta imports from India. Then Delta found its way into Canada from the United States and Europe. Barricades erected against southern Africa yielded a 1.68-fold drop in the Omicron introduction rate, but that gain was "minimized by introductions from the USA."
Estimated SARS-CoV-2 sublineages averted and cases from sublineages averted may seem worth the effort (table below), but percentages of all cases averted in Canada by tightening defenses against each viral variant look less than impressive (table below):
All told, the British Columbia team figured that COVID-directed travel restrictions in Canada may have blocked 264 sublineages from the country and prevented 50,241 cases of infection. But those numbers must be weighed in the context of the currently estimated 4.58 million COVID cases in Canada [2].
"Flight bans and enhanced screening against SARS-CoV-2 variants were most effective when implemented rapidly and for lengthier time," McLaughlin and Joy concluded; "however, effectiveness declined as variants became globally widespread."
References
1. McLaughlin A, Joy JB. Variable reductions in SARS-CoV-2 variant importations following travel restrictions. 30th CROI, Conference on Retroviruses and Opportunistic Infections, February 19-22, 2023, Seattle. Abstract 211.
2. Government of Canada. COVID-19 epidemiology update: Key updates. https://health-infobase.canada.ca/covid-19/ Accessed February 23, 2023.
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