'Super-seeding' drove UK spread of Alpha variant, study shows
The rapid spread of the Alpha variant of SARS-CoV-2 through Britain last autumn was driven by large numbers of infected people exporting the variant to multiple parts of the country, according to a large study. The researchers noted that the explosive spread of the Alpha variant resulted not only from the biological changes in the virus but was also enhanced by the super-seeding event.
Study maps the spread of the variant
The study, published in the journal Science, maps the spread of the variant, from its origins in Kent and Greater London in November 2020 to all but five counties in the UK by January 19 this year. "In December 2020 the epicenter of COVID-19 transmission in England shifted to London and the South East," said study lead author Moritz Kraemer, from Oxford.
Mobility played a significant role in Alpha variant's initial spread
The researchers noted that although travel was curbed after restrictions were introduced on December 20, there was continued exponential growth in Alpha variant cases. The rapid spread of the Alpha variant led to initial reports saying that it could be up to 80 percent more transmissible than the original strain. The study shows mobility significantly affected its spread and early growth rates.
The study explains why the variant spread so quickly
"Estimates of Alpha's transmission advantage over previous strains were initially 80 percent, but declined through time," said Professor Oliver Pybus, from Oxford. "We found Alpha's emergence was a combination of virus genetic changes and transient epidemiological factors. An initial wave of Alpha variant export to places in England with low rates of infection explains why at first it spread so fast," Pybus said.
Origins of variant traced back to South East of England
The researchers said that the Alpha variant does contain genetic changes which makes it more transmissible, and it is likely that the variant was 30 to 40 percent more transmissible than the initial strain. "Our ability to be able to trace the origins of the Alpha back to a point source in the South East of England has important implications," Verity Hill, co-author, said.
