Alpha variant spread quickly as pre-lockdown travel triggered ‘super-seeding event’, study finds

Travel ahead of the PM’s planned Christmas bubble led to a national ‘super-seeding’ event

Joe Middleton
Thursday 22 July 2021 23:32
<p>People at Kings Cross train station in London on December 20</p>

People at Kings Cross train station in London on December 20

The rapid spread of the Covid-19 Alpha variant in Britain during the Autumn last year was a “super-seeding event” that did not slow down until harsh lockdown restrictions were put in place, a new study has revealed.

The proliferation of the virus was driven by biological changes that made it more transmissible, but also because a large amount of people were travelling to different parts of Britain from London and the south-east where it originated.

Researchers said that mobility of the virus did not begin to slow until after Tier 4 Covid restrictions were implemented, but export of the Alpha — or ‘Kent’ — variant did not lessen until early January because of increasing case numbers.

London and the south-east entered the harsher lockdown measures on December 21. In the weeks prior to this the Prime Minister reaffirmed his Christmas “bubble” plan in which three families could mix for up to five days between December 23 and 27.

However due to the spread of the Alpha variant he rapidly curtailed the Christmas plan but didn’t announce the harsher restrictions, or discourage long-distance travel, from London and much of the south and east of England until December 19.

The study, led by Oxford University, and published in the journal Science, maps the spread of the variant ,also known B.1.1.7, from its origins in Kent and Greater London in November 2020.

Dr Moritz Kraemer, lead author on the study and Branco Weiss Research Fellow in Oxford’s Department of Zoology, said: “At the beginning of December 2020 the epicentre of COVID-19 transmission in England shifted rapidly from the North West and North East to London and the South East, as the Alpha variant took hold.

“As people travelled from London and the South East to other areas of the UK they ‘seeded’ new transmission chains of the variant.

“This continued as a national ‘super-seeding’ event which did not start to slow until early January.

“Although travel was curbed, after travel restrictions were introduced on 20 December, this was compensated for by the continued exponential growth in Alpha variant cases.”

Another important finding from the study is that experts overestimated the transmissibility of the Alpha variant, which was thought to be as high as 80 per cent.

But researchers concluded that although the Alpha variant was more transmissible than the original strain, that people moving around the country significantly affected its spread and early growth rates.

Professor Oliver Pybus, lead researcher of the Oxford Martin Programme on Pandemic Genomics, said: “Estimates of Alpha’s transmission advantage over previous strains were initially 80%, but declined through time. 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, from the massive outbreak in Kent and Greater London, explains why at first it spread so fast.

“The Alpha variant does contain genetic changes which makes it more transmissible. It is likely the Alpha variant was 30% to 40% more transmissible than the initial strain. And the early estimates were higher because we did not know how much its growth was exacerbated by human mobility and by how many contacts different groups of people have.

“Crucially, as more variants emerge and spread in other countries worldwide, we must be careful to account for these phenomena when evaluating the intrinsic transmissibility of new variants.”

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