The emergence of a new and more easily spread strain of coronavirus is being blamed for a surge in cases in parts of the UK.
Here we look at how this new strain emerged and what it means for treatments and vaccines.
What is different about the new strain?
Named VUI-202012/01, the new strain has 23 genetic changes, a key one of which is associated with the spike protein, which the coronavirus uses to attach itself to a receptor on human cells. British Prime Minister Boris Johnson said the new strain is up to 70 per cent more transmissible than other strains.
Where did the new strain originate?
UK medical officials think it could have appeared first in London or Kent, a county south-east of London, in September.
But this is not confirmed and it is not even certain that it evolved in the UK. The UK has been particularly good at tracking the evolution of the coronavirus, with figures from late October indicating that it accounted for about half of all coronavirus samples sequenced globally.
This could be why the new strain was identified first in the UK.
Where is it found now?
The new strain is linked to about half or more than half of new infections in London and parts of east and south-east England. It may be why these regions – which now face tougher restrictions to prevent coronavirus spread – have had a surge in cases and hospital admissions.
The strain has, however, also been found in other parts of the UK, albeit at a lower prevalence, including as far afield as Scotland and Wales.
Is it more dangerous?
Prof Chris Whitty, the chief medical officer for England and chief medical adviser to the UK government, said "there is no current evidence" to indicate the new strain causes more serious illness or is more resistant to existing treatments for Covid-19.
Will it render vaccines ineffective?
The evolution of viruses is a key reason why vaccines against them become ineffective. For example, because of the evolution of influenza viruses, different influenza vaccines have to be used each year depending upon which strain is likely to be prevalent in the coming winter flu season.
Vaccines against the new coronavirus often aim to stimulate an immune response against the spike protein, but it is thought there would have to be several changes to the spike protein to make vaccines ineffective. Officials say there is no evidence, as yet, that vaccines being rolled out now will not be effective against the new strain, although further analysis will take place to look at this.
The chief scientific adviser to the UK government, Sir Patrick Vallance, said there were “theoretical reasons” why the new strain may be associated with a different immune response to that linked to other strains.
Why has the coronavirus changed?
All living organisms (including viruses, which exist in a grey area between the living and the non-living) evolve. As they replicate their genetic material, mistakes are made, and these changes can be incorporated into later generations. Some of these genetic changes are inconsequential, but sometimes they result in changes to proteins (which are coded for by genetic material) that make an organism or virus better able to survive, spread or reproduce.
Such beneficial mutations tend to become more prevalent over time, as appears to be happening with the new strain. By contrast, mutations harmful to the organism or virus possessing them are usually weeded out by natural selection.
Is this the first new variant of the coronavirus detected?
No, even before the new strain was identified, researchers had detected many thousands of mutations in the coronavirus’s genome (its complete set of genetic material), including 4,000 affecting the spike protein alone. Most of these changes are insignificant and do not affect the virus’s behaviour.
Another more easily spread variant, known as D614G, has been around for many months and is now the most prevalent form found globally but, like the new variant, is not linked to more severe illness.