Undetected community transmission of Covid-19 took place as early as February in Scotland after the virus entered the country mainly through European travel, researchers have found.
A study led by the University of Glasgow discovered coronavirus was brought to Scotland primarily from countries such as Italy and Spain, with few cases directly linked to China and south-east Asia where the virus is believed to have originated.
Researchers said quarantining travellers from high-risk areas could have prevented the escalation of the outbreak.
The scientists sequenced virus samples from the first confirmed cases of Covid-19 in Scotland.
They found SARS-CoV-2, the virus which causes Covid-19, was introduced hundreds of times during the first four weeks of the outbreak in Scotland, mainly from other European countries.
This predated both UK travel restrictions and extensive restrictions in other European countries.
Advice against travel to mainland China was introduced at the end of January, but the study found cases directly linked to south-east Asia were rare in Scotland.
Quarantine rules for those entering the UK were not introduced until May.
On Thursday, it was announced all travellers to the UK from international destinations will soon have to test negative for coronavirus before they can enter the country.
Samples analysed by researchers included the D614G variant of the virus, which has been associated with increased transmissibility.
Researchers found there was a shift from travel-associated infection of younger adults to community transmission in older adults and healthcare workers within the first month of the pandemic.
Covid-19 was first diagnosed in Scotland on March 1 last year.
During the first month of the outbreak, 2641 confirmed cases of Covid-19 led to more than 1000 people being taken to hospital and 126 deaths – though the report stressed cases were almost certainly higher during this period.
Emma Thomson, the study’s senior author and professor of infectious diseases at the MRC-University of Glasgow Centre for Virus Research, said the virus entered Scotland through at least 283 separate travel-related introductions, leading to community transmission.
“We identified viral lineages with no link to travel as early as three days after the first detection of infection, indicating earlier introduction to Scotland and community spread before the first detected case,” she said.
“The emergence of continental Europe as the epicentre of the global Covid pandemic was a clear driver of the Scottish outbreak, with the majority of the lineages detected in this study related to European sequences.
“Cases with links to China and other countries in south-east Asia were comparatively not detected.
“The speed at which the virus took hold in Scotland and the UK as a whole, following multiple introductions, mainly from other European countries, was extremely rapid.
“It is possible an earlier lockdown from countries with a high burden of cases, such as Italy, and other measures such as quarantine of travellers from high-risk areas might have prevented escalation of the outbreak and multiple clusters of ongoing community transmission.”
The University of Glasgow worked with the West of Scotland Specialist Virology Centre, the Royal Infirmary of Edinburgh and researchers at the University of Edinburgh on the study.
The findings, in the study “Genomic epidemiology reveals multiple introductions of SARS-CoV-2 from 3 mainland Europe into Scotland”, are published in Nature Microbiology.