Indications the mutant coronavirus variant which emerged in the south of England may be more deadly and be more transmissible are a “serious turn for the worse”, a leading scientist has said.

Data suggests that for a thousand people in that group who became infected with the old variant, roughly 10 would be expected to die – whereas with the new variant it might be 13 or 14, with similar increases in mortality rates across the age ranges.

A paper from the New And Emerging Respiratory Virus Threats Advisory Group (Nervtag), published on Friday, said there was a “realistic possibility” that the variant is associated with an increased risk of death.

But it also stressed that the “absolute risk of death per infection remains low”.

John Edmunds, professor in the Centre for the Mathematical Modelling of Infectious Diseases at the London School of Hygiene and Tropical Medicine and a member of Nervtag, said: “If the case fatality ratio stayed the same, an increase in transmissibility is worse than a corresponding increase in case fatality because you have an expanding epidemic, and so more and more cases.

“Unfortunately, it looks as if this virus might be both – certainly increased transmissibility compared with the previous strains that we were dealing with, and it looks as if unfortunately it may also increase fatality as well, so it’s really a serious turn for the worse unfortunately.”

Echo: Data shows the new variant is more prominent in London and the South EastData shows the new variant is more prominent in London and the South East

Graham Medley, professor of infectious disease modelling at the London School of Hygiene and Tropical Medicine, said that despite the uncertainty of the data, it is clear the new strain is not more benign.

He explained: “One of the possibilities was that this new variant would cause less mortality, it would be less virulent.

“And I think we can be absolutely sure that’s not the case.

“Whether there is a significant increase in mortality – the evidence we have is very solid but it still could be wrong with different data or change with different data sets, but it’s certainly not the case that this is a more benign virus.”

The experts also said that despite the data suggesting the mutant variant may be more deadly, there is no evidence to indicate existing treatments, like dexamethasone, will not be effective against it.

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Peter Horby, professor of emerging infectious diseases at the University of Oxford, and chairman of Nervtag, said: “The core principles of control remain exactly the same for this virus as the old variants.

“There’s no evidence that this new virus is evading any of the treatments that have been found to work or any of the vaccines.

“It just highlights the importance of continuing to drive down the numbers of infections occurring.”

Prof Medley said it is “critical” to reduce the incidence of infection, and that the new results do not suggest anything needs to be done differently.

He added: “Whether or not you then want to make sure the incidence comes down further by either strengthening lockdowns or increasing the duration of a lockdown, I think it’s totally up to the Government to decide that.

“But it’s not that this new result suggests that we need to do anything hugely different – we’re still faced with the same as far as the NHS for the same urgency.”