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expert reaction to brief summary of NERVTAG opinion from the NERVTAG meeting on SARS-CoV-2 variant under investigation VUI-202012/01

A New and Emerging Respiratory Virus Threats Advisory Group (NERVTAG) meeting on the SARS-CoV-2 variant under investigation, VUI-202012/01, took place on the 18 December.


Prof Martin Hibberd, Professor of Emerging Infectious Disease, London School of Hygiene & Tropical Medicine (LSHTM), said:

“With so many SARS-CoV-2 infections in the world, it is not unexpected that new strains may occur and compete for selective advantage. And it seems that the intensive surveillance programme undertaken by the UKs ICOG sequencing consortium (as part of a larger worldwide effort), has now identified a distinctive cluster of viruses, that they have termed the ‘B.1.1.7 lineage’. This lineage seems to be the first to be identified that has acquired a number of mutations that differentiate it from other viruses that have been reported around the world. Worryingly, several of these mutations may have functional significance. While new mutations occur at a steady rate, they have not, until B.1.1.7, accumulated into a single strain, suggesting that this new variant has acquired them through selection for improved properties. As viruses are transmitted, those that allow for increased virological ‘success’ can be selected for, which changes the properties of the virus over time. This typically leads to more transmission and less virulence and for human infecting coronaviruses the end result of this evolutionary process might look like the other 4 commonly found coronaviruses that cause symptoms that we recognise as the common cold – however, these 4 common cold viruses are highly contagious. The new B.1.1.7 may be on the path towards this but is not there yet, and still appears to have all the human lethality that the original had but with an increased ability to transmit. Hopefully, it does not alter the immune response sufficiently to interfere with the vaccine protection. While the consequences of this new strain are still being worked out, it seems prudent to try to reduce its spread around the UK and the rest of the world.”


Prof Rowland Kao, Royal (Dick) School of Veterinary Studies and Roslin Institute, University of Edinburgh, said:

“There appear to be at least two lines of evidence for showing that the strain is more transmissible. First, by comparing the number of observed copies of the variant strain (i.e. virus taken from infected people with the identical or near-identical type) to the number of copies of different strains circulating in the same area, you can estimate directly the rate at which the type is reproducing itself compared to others. However this is reliant on having a good number of samples that capture the new variant and other types in reasonably close proportion to each other.  

“Second, you can estimate the reproduction number R, around where the variants are, and compare it to the R number elsewhere, however this is less precise because you don’t always know what is causing the new cases (is it the new variant or another type?). The fact that these two lines of evidence give similar increases in transmissibility makes the overall case more robust. That the increase in transmission is so high (the central estimate being perhaps 70% higher) is a cause for some considerable concern, as reflected in the increasing transmission even when under Tier 3 restrictions.

“Of additional concern is that many people who were aiming to travel for the Christmas break likely would have already done so; add-in the anecdotal reports of people rushing to travel before restrictions, and this raises the possibility that travel bans are already too late to have prevented widespread circulation of the new variant across the UK, spread that will only increase due to people returning to their non-holiday places of residence, after the break. While it remains possible that this variant is actually less likely to cause severe illness, we shall not know one way or another for some time. In the meantime, the implications for this (less effectiveness of lower level tiers, more vaccinations needed to achieve herd immunity, for example) imply that these restrictions may be in place for some time, possibly at least until vaccination is able to achieve good protection of the most vulnerable.”


Dr Julian Tang, Honorary Associate Professor/Clinical Virologist, University of Leicester, said:

“The spread of this new virus variant could be due to many factors.  As we saw with the earlier D614G variant – just higher viral loads in clinical diagnostic swabs or in cell culture may not necessarily translate to a more transmissible virus at the population level.

“A higher genomic growth rate in the samples sequenced, may not necessarily mean higher transmissibility, e.g. if there was a rave of several thousand people where this variant was introduced and infected many people mostly in that rave, this may seem very high compared to a lower background of non-variant virus, e.g. in an otherwise prevailing national lockdown.

“The NERVTAG team appear to be being very careful about such comparisons – and possible ‘founder effects’ that might be misleading – which is good.

“At least two of the mutations in this new variant, N501Y (since at least Apr 2020 in Brazil) and 69-70del (since at least Jan/Feb 2020 in Thailand/Germany) were already circulating globally prior to combining into this new variant.

“This is quite normal for viruses – like influenza – where different viruses may infect the same person, leading to a hybrid virus emerging.  This is just one of the ways that natural viral variation arises.

“We are not seeing any increased virulence (clinical severity) or any gross changes in the S (spike protein) that will reduce vaccine effectiveness – so far.

“New viruses will adapt to a new host over time – with decreasing mortality, and possibly increasing transmissibility.

“It makes no sense for the virus to kill its host – rather better for it to replicate to high levels in the host, causing few symptoms – so that the host can stay mobile and appear well (asymptomatic) – to allow it to mingle further with those who are still susceptible – and spread its genes further.

“We are now likely seeing some of this new host adaptation process in SARS-COV-2, but it remains to be seen whether mortality will be different with this variant than with the previous one.”



All our previous output on this subject can be seen at this weblink:



Declared interests

Prof Martin Hibberd: I have no conflicts to declare, but I am a member of the COG-UK consortium, although I was not involved in any of the work prepared for the NERVTAG papers.

None others received.

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