A variant of the coronavirus that is thought to have emerged in Kent may be more than 100% deadlier than previous versions of the infection, research suggests.
After being identified towards the end of 2020, the so-called Kent variant – also known as B.1.1.7 – quickly became the UK's dominant coronavirus, prompting English officials to introduce a third lockdown at the start of 2021.
Studies have shown the variant's mutations enable it to spread more readily, however, experts were less clear whether it caused more severe complications.
To learn more, scientists from the universities of Exeter and Bristol analysed more than 54,000 people who tested positive for the Kent variant in the community and a further 54,000 who had a previous version of the virus.
Results reveal 227 deaths occurred among those with the Kent variant, compared to 141 in the individuals with an earlier version of the infection.
The scientists concluded the Kent variant appears to raise an adult's likelihood of dying with the coronavirus by 32% to 104%, but stressed the risk "remains relatively low".
"In the community, death from COVID-19 [the disease caused by the coronavirus] is still a rare event, but the B.1.1.7 variant raises the risk," said lead author Dr Robert Challen, from the University of Exeter.
"Coupled with its ability to spread rapidly this makes B.1.1.7 a threat that should be taken seriously."
The scientists compared people, aged over 30, who swabbed positive for the Kent variant or an older version of the coronavirus in the community.
The participants were matched according to factors like their age, ethnicity and level of "deprivation".
"We focussed our analysis on cases that occurred between November 2020 and January 2021, when both the old variants and the new variant were present in the UK," said study author Dr Leon Danon, from the University of Bristol.
"This meant we were able to maximise the number of 'matches' and reduce the impact of other biases."
The participants were followed until 12 February.
The results reveal those infected with the Kent variant were between 32% and 104% more likely to die within 28 days of a positive test.
"This represents an increase in deaths from 2.5 to 4.1 per 1,000 detected cases," which is still "relatively low", the scientists wrote in The BMJ.
When averaged out, the most "probable" increased death risk was found to be 64%.
"Subsequent analyses have confirmed our results," said Dr Danon.
Early data from the London School of Hygiene and Tropical Medicine and Imperial College London have also suggested an increased death risk with the Kent variant, as reported by the government's New and Emerging Respiratory Virus Threats Advisory Group (Nervtag).
Watch: Do coronavirus vaccines affect fertility?
Viral mutations are not unexpected, with the majority having a neutral effect. Those that benefit the virus' transmission may "stick", think survival of the fittest.
Genetic sequencing has shown the Kent variant has 14 mutations, eight of which affect its spike protein, which the coronavirus uses to enter cells.
By changing the "binding mechanism", the virus has "the potential for increased infectivity", making the outbreak harder to control.
"The variant of concern, in addition to being more transmissible, seems to be more lethal," wrote the scientists.
"We expect this to be associated with changes in its phenotypic properties because of multiple genetic mutations."
Concerns have also been raised mutated coronaviruses may not respond to the long-awaited vaccines, which have been hailed our route back to life as we once knew it.
Research suggests emerging variants of the coronavirus – including the Kent one – do respond to the jabs being rolled out, but perhaps to a lesser extent.
"[The coronavirus] appears able to mutate quickly and there is a real concern other variants will arise with resistance to rapidly rolled out vaccines," said Dr Danon.
"Monitoring for new variants as they arise, measuring their characteristics and acting appropriately needs to be a key part of the public health response in the future."
The Kent variant has been identified in more than 50 countries, with the scientists stressing they "see no reason" why their results would only apply to the UK.
"Healthcare capacity planning, and national and international control policies are all impacted by this finding, with increased mortality lending weight to the argument further coordinated and stringent measures are justified to reduce deaths from [the coronavirus]," they wrote.
Not everyone is convinced by the study, however, with the scientists not adjusting for underlying health issues that can make coronavirus complications more severe.
"Clinical teams know the coldest winter temperatures occurring in Jan/Feb can exacerbate all the co-morbidities that predispose to more severe outcomes of COVID-19 – like chronic heart, lung, renal [and] neurological diseases," said Dr Julian Tang, from the University of Leicester.
"So without the careful matching of co-morbidities, these differential clinical severity model outcomes are still questionable.
"We really need to revisit this in spring to account for the cold weather factor and there are also other seasonal variables related to shorter daylight hours."
Timing the study around England's third lockdown may have also led to "confounders".
"Lack of exercise, increased consumption of junk food, stresses related to home schooling, increased and prolonged economic stress, ongoing lack of attendance for other healthcare problems; which may impact on various host immune responses to these viruses," added Dr Tang.
Watch: Can you catch coronavirus twice?