Canada’s international travel restrictions reduced the number of coronavirus cases entering the country during the first waves of the pandemic, but did not prevent new cases, according to a new study. The study, led by University of British Columbia (UBC) researchers, finds that cases of COVID-19 dropped 10-fold four weeks after new restrictions prevented most foreign nationals from entering the country in March 2020. The researchers constructed a detailed timeline of how the virus entered the country from January 2020 to March 201, using publicly available viral genome sequences. The data was used to determine the geographic origin of the COVID-19 cases, allowing the identification of 2,263 cases where it was introduced. The study, published today in eLife, is the first nationwide genomic analysis of COVID-19 epidemiology in Canada. “Imports of COVID-19 were accelerating until March 2020, but experienced a sharp and drastic decline after travel restrictions were imposed,” said UBC’s Angela McLaughlin, Ph.D. candidate in bioinformatics and lead author of the study. “The data show that federal travel restrictions can be effective in reducing virus imports when implemented quickly.” But while the restrictions have reduced the introduction of the virus, they have not eliminated it. Instead, they continued “at a lower level in the spring and summer of 2020,” the study notes. These new transmission chains contributed to Canada’s second wave and rebounded further in November. In addition, relaxed entry requirements led to emerging variants of concern (VOC) and interest (VOI). “Travel restrictions have diminishing returns if domestic transmission is high, if highly transmissible variants become widespread globally, or if there are many people exempt from travel restrictions and quarantine without access to rapid testing,” McLaughlin said.
Public health interventions to prevent the spread of COVID-19
The study notes that an estimated 30 unique genetic sublines of the Alpha variant (B.1.1.7) were introduced into Canada by February 2021. From there, these sublines increasingly displaced the original strain of COVID-19 during the second half of second wave and third wave. The only way to fully limit the introduction of new cases would be to continue travel restrictions. But continuing to enforce the rules carries a significant financial burden, according to the researchers. “The social and economic impacts of travel restrictions must be weighed against the risk of unfettered virus introduction, which has the potential to overburden the health care system,” McLaughlin explained. During Canada’s first wave, data suggest that 49 percent of cases likely originated in the United States and were mostly imported into Quebec and Ontario. In the second wave, the United States continued to be the “dominant source of virus entry, at 43 percent, alongside a larger contribution from India, 16 percent and [United Kingdom]to seven percent.” The study was conducted by researchers at UBC and the BC Center for Excellence in HIV/AIDS (BC-CfE), along with colleagues from Western University, the University of Arizona and the Canadian COVID-19 Genomics Network (CanCOGeN). According to the researchers, the study provides key information about the “effectiveness of public health interventions” that enable policymakers to respond to viral threats in the future.
