How has the UK-derived SARS-CoV-2 mutant strain spread internationally?

Researchers analyzed Facebook-based mobility data and found that travelers from the UK may have spread the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) strain that originated there to at least 16 countries by the beginning of December 2020.

A new variant of SARS-CoV-2 emerged in the United Kingdom (UK) in the latter half of 2020. The first report of this new strain was from samples in Kent on 20 September and in London on 21 September. This new variant is associated with increased transmissibility of the virus, though no evident has come to light as yet of increased virulence or pathogenicity.

In the middle of December, the UK government placed stringent measures in London and southeast England to curb its transmission. Beginning 5 January, the country has re-imposed a nationwide lockdown, closing schools and non-essential businesses until mid-February.

Although several countries had imposed restrictions on travel from the UK by 20 December, the new virus variant has been detected in many countries including the USA, Sweden, and India.

A team of international researchers collected data from 19 countries to determine the probability that the new virus variant was introduced into these countries by travelers from UK and local transmission thereon. They reported their results on the medRxiv* preprint server.

New virus strain could have been spreading globally for months

Using mobility data from Facebook Data for Good, the team estimated the probability that at least one person infected with the new SARS-CoV-2 variant arrived from the UK.

They found Ireland had the highest risk of importing the new strain between 22 September and 7 December 2020, while Hungary had the lowest risk. About a month after the new mutant strain was discovered in the UK, there was at least a 50% chance that 13 of the 19 countries the authors studied had one case imported from the UK. By 1 November 2020, Turkey, Bulgaria, and Cyprus exceeded this probability threshold, while the United Arab Emirates, Sweden, and Hungary were still below the threshold point.

Estimated risks for introduction of the 501Y variant of SARS-CoV-2 from the UK to other 19 countries before December 7, 2020. (A) The probability that at least one person infected with the new COVID-19 variant has arrived at the target country from the UK by the date indicated on the x-axis, based on Facebook mobility data. (B) Estimated daily prevalence of the 501Y variant of SARS-CoV-2 in 19 countries between September 22 and December 7, 2020, assuming that the variant is = 50% more transmissible than the 501N variant (5). Points and bars indicate means and standard deviation based on 100 simulations. (C) Risk of at least one importation by November 1, 2020 (also indicated as line colors in A). The 16 countries above and 3 countries below the risk threshold of 50% are indicated in red and bluegreen, respectively. Grey indicates countries/regions where mobility data were not available.
Estimated risks for introduction of the 501Y variant of SARS-CoV-2 from the UK to other 19 countries before December 7, 2020. (A) The probability that at least one person infected with the new COVID-19 variant has arrived at the target country from the UK by the date indicated on the x-axis, based on Facebook mobility data. (B) Estimated daily prevalence of the 501Y variant of SARS-CoV-2 in 19 countries between September 22 and December 7, 2020, assuming that the variant is = 50% more transmissible than the 501N variant (5). Points and bars indicate means and standard deviation based on 100 simulations. (C) Risk of at least one importation by November 1, 2020 (also indicated as line colors in A). The 16 countries above and 3 countries below the risk threshold of 50% are indicated in red and bluegreen, respectively. Grey indicates countries/regions where mobility data were not available.

Next, the team used COVID-19 hospital admission data to estimate how the new strain spread locally in 11 countries, assuming the new variant is 50% more transmissible than the earlier circulating strain, 501N.

The spread was fastest in Ireland before it slowed down in November 2020. It is expected that in other countries also the spread is rapid. Italy had the highest prevalence of the new strain as of 7 December 2020.

These projections suggested that countries with substantial population movement from the UK were likely to harbor cases of the new variant by late October, 2020,” write the authors.

However, the results may have limitations. The Facebook mobility estimates may be biased by the demographics of users. The authors assumed a 9.5-day between infection and hospitalization based in estimates from the United States. So, the projections will need to be refined further as more data comes in in the future.

In conclusion, the authors write, “However, our findings should be robust in suggesting that the new virus variant has likely been introduced by travelers from the UK and spreading undetected for months in many countries.”

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
Lakshmi Supriya

Written by

Lakshmi Supriya

Lakshmi Supriya got her BSc in Industrial Chemistry from IIT Kharagpur (India) and a Ph.D. in Polymer Science and Engineering from Virginia Tech (USA).

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