21 December 2020


Special Report


  • Rapid growth of new SARS-CoV-2 variant in UK raises credible concerns of increased transmission, but vaccines will very likely remain effective
  • Widespread travel bans will likely remain in place until end of year, but new variant will probably already be circulating widely beyond UK
  • Affected countries will need to implement stricter lockdowns if increased transmissibility of new variant is confirmed



UK Prime Minister Boris Johnson announced on 19 December that London and many areas across the southeast and east of England would be placed under harsher “tier 4” coronavirus (COVID-19) restrictions from 20 December, prohibiting gatherings over Christmas. The devolved administrations also introduced tighter restrictions across the rest of the UK. These moves were prompted by growing fears over the rapid rise in prevalence of a new variant of SARS-CoV-2, the virus that causes COVID-19, named B.1.1.7 (or VUI-202012/01), which was first isolated in September.

Following Johnson’s announcement, the UK’s New and Emerging Respiratory Virus Threats Advisory Group (NERVTAG) published minutes summarising the advice that had informed the government’s decision, noting an estimated 71% increase in B.1.1.7’s growth rate versus other variants. In practical terms, NERVTAG stated that this could increase the rate of transmission – R, a measure of how many people an infected individual would be expected to infect – from 0.39 to 0.93. Concerns over the spread prompted many countries, principally in Europe, to begin introducing travel bans on the UK as of 20 December. The most significant was imposed by France, which blocked passenger and freight transport from the UK for 48 hours from midnight on 20 December, effectively halting Dover-Calais trade.


Mutation is common in viruses. The process is however highly unpredictable, and not all such changes will materially alter the virus’ behaviour. Indeed, many changes are ultimately neutral, while others either hinder or benefit the virus. Numerous genetically distinct strains of SARS-CoV-2 have circulated since the pandemic began, producing little evidence of any behavioural change. This reflects its relative stability, with the virus typically accruing just one or two mutations per month. Part of the reason that B.1.1.7 has raised such acute concerns is that it rapidly developed 23 mutations, including 17 that are plausibly capable of altering behaviour. This likely resulted from the virus having a longer opportunity to undergo mutation within an immunocompromised host who was unable to clear the infection efficiently. The speed with which B.1.1.7 has become the dominant variant by displacing other strains in London and surrounding areas, reflected in data surveys, will also have raised…

Source: UK Office for National Statistics
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