Genomic epidemiology reveals multiple introductions of SARS-CoV-2 from mainland Europe into Scotland

Genomic epidemiology reveals multiple travel-related introductions of SARS-CoV-2 from mainland Europe into Scotland during the first wave of COVID-19. Coronavirus disease 2019 (COVID-19) was first diagnosed in Scotland on 1 March 2020. During the first month of the outbreak, 2,641 cases of COVID-19 led to 1,832 hospital admissions, 207 intensive care admissions and 126 deaths. We aimed to identify the source and number of introductions of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) into Scotland using a combined phylogenetic and epidemiological approach. Sequencing of 1,314 SARS-CoV-2 viral genomes from available patient samples enabled us to estimate that SARS-CoV-2 was introduced to Scotland on at least 283 occasions during February and March 2020. Epidemiological analysis confirmed that early introductions of SARS-CoV-2 originated from mainland Europe (the majority from Italy and Spain). We identified subsequent early outbreaks in the community, within healthcare facilities and at an international conference. Community transmission occurred after 2 March, 3 weeks before control measures were introduced. Earlier travel restrictions or quarantine measures, both locally and internationally, would have reduced the number of COVID-19 cases in Scotland. The risk of multiple reintroduction events in future waves of infection remains high in the absence of population immunity.

Automated summary

Genomic epidemiology analysis revealed multiple introductions of SARS-CoV-2 into Scotland from mainland Europe, especially Italy and Spain, during the first wave of COVID-19. Early introductions led to community outbreaks, healthcare facility transmission, and an outbreak at an international conference. Earlier implementation of travel restrictions and quarantine measures could have reduced the number of COVID-19 cases in Scotland.