‘Super-seeding’ drove UK spread of Alpha variant, study shows

The explosive spread of the Alpha coronavirus variant across Britain last autumn was a “super-seeding event”, a major international study has shown.

It was not only driven by biological changes that made the virus transmissible, but also by the large number of infected people who transported Alpha across the country from London and south-east England, where it originated.

The research, led by the University of Oxford, combined extensive genetic analyzes of Covid-19 samples with human mobility data to determine the way in which Alpha – formerly known as B.1.1.7 or the Kent variant – Covid-19 cases in dominate the UK, to map. within four months.

The study, published in Science On Thursday, it could be a model to track the future emergence of virus variants and other new pathogens, the authors said.

An important finding was that experts initially overestimated how much more transmissible Alpha was because they did not appreciate the extent to which human behavior and movements of humans promoted its spread.

Animated map showing the distribution of the Alpha variant in the United Kingdom

“Estimates of Alpha’s transfer advantage over previous strains were initially 80 percent, but have declined over time,” said Oliver Pybus, lead researcher on the Oxford Martin program on pandemic genomics.

“While people from London and the south-east traveled to other areas in the UK, they ‘sowed’ new transmission chains of the variant,” explains Moritz Kraemer of Oxford University, lead author of the Science article. continued as a national ‘super-seeding’ event that only began to slow down in early January. ‘

The current estimate is that Alpha is 30 to 40 percent more transmissible than the earlier strains of Sars-Cov-2 that replaced it, Pybus added.

According to scientists, their study emphasizes the importance of combining different surveillance methods to detect the emergence of new pathogens.

“Only through the integration of high-resolution genomics, case testing and anonymous mobility data have we been able to identify the drivers of alpha emergence and distribution in the UK,” said Samuel Scarpino, a disease modeler at Northeastern University in Boston, who was part of the project team.

“The discovery of the mechanisms of B.1.1.7 emergence enables governments to respond more effectively and promotes our scientific understanding of epidemics,” Scarpino said. “The challenge now is to build similar surveillance systems worldwide.”

Researchers have begun applying similar techniques to other rapidly evolving new variants, most notably Delta, which originated in India and has so far been widely regarded as the most dangerous manifestation of Sars-Cov-2, due to its transmissibility and potential for bypassing vaccines.

Graph showing the estimated number of weekly exports of descent B.1.1.7 from the Greater London area

They believe similar “super-seeding”, caused by thousands of people who flew into the UK before a travel ban was imposed from India on April 23, accelerated the spread of Delta through Britain and the rest of Europe, although no comprehensive analysis of this process has yet to be published.

“As new variants appear, we expect it to spread significantly before travel restrictions are introduced, as probably happened with the Delta variant,” Kraemer said.

“Given the scale of the current outbreak, it appears likely that the UK is now a major exporter of the Delta variant across Europe and other parts of the world.”

Delta has almost completely replaced Alpha in the UK. The most recent report from Public Health England shows that during the week to July 14, there were 36,000 new cases of Delta and 453 of Alpha.

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