RESUMEN
Background: Retrospectively quantifying effectiveness of interventions such as travel restrictions to counter viral introduction and transmission is critical to inform public health policy. Phylogenetic analyses of SARS-CoV-2 variants were undertaken to quantify the effects Canadian COVID-19 travel restrictions had on variant importation and transmission dynamics. Method(s): Global and Canadian GISAID sequences available up to March 2022 were subsampled proportionally to variant-specific case counts and ten phylogenies were inferred for each variant. Trees, dates, and geographies were inferred using maximum likelihood. Result(s): In response to Alpha, Canada implemented a UK flight ban from December 20, 2020-January 6, 2021, resulting in a 1.5-fold reduction in UK sublineage importation rate, with subsequent rebound (Fig. 1). Enhanced screening measures were implemented on December 24, 2020 for South African arrivals to counter Beta. Although there was a 6.3-fold reduction of Beta sublineages per week from South Africa following enhanced screening, there is low confidence in rare events. For Gamma, enhanced screening for arrivals from Brazil was implemented March 31-April 13, 2021. Proportion of Gamma sublineages from Brazil was reduced 1.6-fold within 2 weeks of the intervention, but the weekly importation rate was not significantly changed from start to end of intervention. In response to Delta, Canada issued a suspension of flights from India from April 22-September 23, 202, coinciding with a 2.4-fold reduction in sublineage importation and 3.8-fold reduction in proportion of sublineages from India. Increased importations from the USA and Europe progressively negated the ban's effectiveness. Against Omicron, Canada banned entry of all foreign nationals who had travelled through southern Africa and implemented enhanced screening for Canadians from November 26- December 18, 2021. Subsequently, the BA.1 sublineage importation rate from South Africa was maintained at a low level amid rising cases, while importations from other sources increased, reducing the proportion of sublineages from South Africa and diluting the measure's effectiveness. Conclusion(s): Flight bans and enhanced screening against SARS-CoV-2 variants were most effective when implemented rapidly and for lengthier time;however, effectiveness declined as variants became globally widespread. Ongoing genomic surveillance programs incorporating phylodynamic analyses can inform travel restriction and non-pharmaceutical intervention policy. (Figure Presented).