The new strain of the coronavirus identified in the United Kingdom could be not only more transmissible but also more deadly, British Prime Minister Boris Johnson said on Friday.
"It also now appears that there is some evidence that the new variant ... may be associated with a higher degree of mortality," he said at a Downing Street news conference.
Chief government scientist Patrick Vallance said the new variant could be around 30% more deadly, although he stressed that only sparse data were available.
He said that for a 60-year-old man, around 10 in 1,000 would be expected to die after catching the original strain.
But that rises to "13 or 14" for the new strain.
"You will see that across the different age groups as well, a similar sort of relative increase in the risk," he added.
Britain is in the grip of its third and worst wave of the virus, recording record daily death tolls that have pushed the total figure close to 100,000.
Another 1,401 people were announced on Friday to have died within 28 days of testing positive, bringing the total to 95,981.
More than 38,500 people were in the hospital with COVID-19 – 78% more than during the first peak last year.
On average, one in 55 people have got the virus in England, rising to one in 35 in London, said chief medical officer Chris Whitty.
Although cases appear to have leveled off, hospitals are in danger of becoming overwhelmed and the government is in a race to vaccinate as many vulnerable people as possible.
Johnson said some 5.3 million people had received their first jab, and the government was on track to achieve its target of vaccinating 15 million of the most vulnerable by mid-February.
Vallance said there was "increasing evidence" that the AstraZeneca/Oxford and Pfizer vaccines being used in Britain were both effective against the new strain.