There were more than 1,000 introductions of the novel coronavirus in the UK during the first wave of the Covid-19 pandemic, scientists have found.
The highest number of transmission chains during the first half of 2020 were from Spain (33%), according to the researchers, with France accounting for 29% of the imports and Italy 12%.
China, meanwhile, was responsible for only 0.4% of the introduction in the UK.
Based on the findings, published in the journal Science, the researchers said earlier travel and quarantine interventions could have helped reduce the intensity of the UK’s first wave of cases.
Professor Oliver Pybus, from the University of Oxford’s Department of Zoology and the Oxford Martin School, who is co-lead author on the study, said: “This study shows that it’s possible to trace individual virus transmission lineages accurately through time and space.
“Undertaking analyses on a weekly basis means that genomic tracking can become a key component of public health surveillance.”
He added: “By reconstructing where and when Covid-19 was introduced to the UK we can see that earlier travel and quarantine interventions could have helped to reduce the acceleration and intensity of the UK’s first wave of cases.”
Their analysis is based on more than 50,000 genomes, or genetic material, of Sars-Cov-2, the virus that causes Covid-19, that was available before June 26 2020.
Around 26,000 of the genomes in the study came from the UK’s Covid-19 Genomics UK (COG-UK) consortium.
These coronavirus introductions, via infected travellers from overseas, lead to distinct virus lineages circulating in the UK, which were distinguishable by one or more mutations.
The researchers said that their work offers “a never-before-seen level of insight into the origins and behaviour of transmission chains since the start of the pandemic”.
They said that high travel volumes and few restrictions on international arrivals before the March 2020 lockdown “led to the establishment and co-circulation of more than 1,000 identifiable UK transmission lineages”.
The team said this “contributed to accelerated epidemic growth that quickly exceeded national contact tracing capacity”.
The experts also said their findings offer a crucial context to what is currently happening in the UK’s second wave as a new coronavirus variant, dubbed B.1.1.7 and VUI – 202012/01, continues to rapidly grow across the country.
They believe that a detailed comparison of the new variant’s behaviour with that of coronavirus lineages from the first wave will help understand why B.1.1.7 is spreading so quickly.
Co-lead author Louis du Plessis, a postdoctoral researcher at Oxford’s Department of Zoology, said: “Our work offers unparalleled views into what’s happening in an individual epidemic.
“The UK shares large volumes of virus genetic data publicly on a weekly basis and if you don’t have this level of surveillance you won’t know the real situation of virus evolution and transmission.
Commenting on the research, Ed Feil, professor of microbial evolution at the University of Bath, said: “With respect to the current outbreak, the work confirms the importance of early interventions in snuffing out newly introduced lineages before they get a chance to become widespread.
“Perhaps more importantly, however, the analysis provides an excellent roadmap and exemplar for how large genome sequence datasets can help lay bare in exquisite detail the anatomy of an epidemic.”