New variants of coronavirus have been emerging and circulating around the world.
Some of them appear to be more contagious and may escape some of the protection offered by past infection or vaccination.
Experts are closely studying them to understand if vaccines may be need to be updated to be a better match.
What are these new variants?
There are many thousands of different versions, or variants, of Covid circulating.
- A UK or Kent variant (also known as B.1.1.7) now dominant in much of Britain, has spread to more than 50 countries and appears to be mutating again
- A South Africa variant (B.1.351) found in at least 20 other countries, including the UK
- A Brazil variant (also known as P.1) detected in four travellers to Japan which has now been found in the UK
It's not unexpected that new variants have developed - all viruses mutate as they make copies of themselves to spread and thrive.
Most of these differences are inconsequential. A few can even be harmful to the virus's survival. But some can make it more infectious or threatening.
Are the new ones more dangerous?
There is no evidence that any of them cause much more serious illness for the vast majority of people who become infected.
As with the original version, the risk is highest for people who are elderly or have significant underlying health conditions.
Measures such as washing your hands, keeping your distance from other people and wearing a face covering will still help prevent infections. Because the new variants appear to spread more easily it is important to be extra vigilant.
What's happening to the virus?
The UK, South Africa and Brazil variants could be much more contagious or easy to catch.
All three have undergone changes to their spike protein - the part of the virus which attaches to human cells.
As a result, they seem to be better at infecting cells and spreading.
Experts think the UK or "Kent" strain emerged in September and may be up to 70% more transmissible or infectious. Research by Public Health England puts it between 30% and 50%.
The South Africa variant emerged in October, and has more potentially important changes in the spike protein. Experts recently found a small number of cases of the UK variant that have one of these more concerning changes too.
It involves a key mutation - called E484K - that may help the virus evade parts of the immune system, called antibodies, that can fight coronavirus based on experience from prior infection or a vaccine.
The Brazil variant emerged in July and has this E484K mutation too.
Will vaccines still work?
Current vaccines were designed around earlier versions of coronavirus, but scientists believe they should still work, although perhaps not quite as well.
A recent study suggests the Brazilian variant may be resisting antibodies in people who should have some immunity because they have caught and recovered from an earlier version of coronavirus.
Early results from Moderna suggest its vaccine is effective against the South Africa variant, although the immune response may not be as strong or long-lasting.
Variants could emerge in the future that are different again.
Even in the worst case scenario, vaccines could be redesigned and tweaked to be a better match - in a matter of weeks or months, if necessary, say experts.
As with flu, where a new shot is given each year to account for any changes in circulating flu viruses, something similar could happen for coronavirus.
What is being done about it?
More variants will emerge.
Scientists around the world are on the look-out and any important ones will be closely studied and monitored.
Experts are updating coronavirus vaccines. The UK Government has announced a deal with biopharmaceutical company CureVac to develop vaccines against future variants, with a pre-order of 50 million doses.