The prime minister told a Downing Street briefing: “We’ve been informed today that, in addition to spreading more quickly, it also now appears that there is some evidence that the new variant, the variant that was first identified in London and the south-east, may be associated with a higher degree of mortality.”
Chief scientific adviser Sir Patrick Vallance revealed that with the original strain of Covid-19, roughly 10 out of every 1,000 men in their 60s who get infected would be expected to die.
With the new variant, this risk would rise to roughly 13 or 14 out of every 1,000.
Vallance however stressed that the data was “currently uncertain”, but conceded “obviously this is a concern”.
Both Johnson and Vallance stressed that current evidence suggests vaccines will work on the new variant, which transmits between 30% to 70% more easily.
The PM said: “All current evidence continues to show that both the vaccines we’re currently using remain effective both against the old variant and this new variant.”
Vallance said the Brazilian and South African coronavirus variants are of more concern than the UK strain because there are fears they may be less susceptible to vaccines.
Public Health England has estimated that 44 people in the UK have the South African variant, with a maximum estimate of 71 people being infected with it, he added.
The chief scientific adviser said: “We know less about how much more transmissible they are.
“We are more concerned that they have certain features that they might be less susceptible to vaccines.”
Johnson defended the current restrictions, insisting they are “the right package of measures to deal with the new variant” and stressing public compliance with them is “the crucial thing”.
The PM also pointed to falling new case numbers as evidence the lockdown was adequate.
“There are signs that this is working but it’s going to need continued resolve and determination,” he said.
But he acknowledged: “It is an open question as to when and in what way you can start to relax any of the measures.
“It depends entirely on lots of different things – it depends on the vaccine rollout continuing to go well, it depends on there being no further discoveries about what new variants can do, it depends most of all on getting the overall incidence down from a level at which it can’t just tick off again in the way that we’ve seen it do before.”
Johnson also hinted that he wants this to be the final Covid lockdown.
He said: “The British public and British business would much rather we opened safely and cautiously when it was right to do so, rather than opening up again and then being forced to close back down simply because the virus takes off.”
England’s chief medical officer Chris Whitty also warned that although overall cases are falling, among certain groups such as 20 to 30 year-olds infections might be rising.
Cases are also “very high and very precarious” and if people let their guard down the NHS could be in “really deep trouble”, he added.