Coronavirus has been changing in ways that might help it escape some of the body's immune system defences.
Scientists are working to update the Oxford-AstraZeneca vaccine, as research suggests it - and other coronavirus vaccines - may be less effective against the South Africa variant.
The ones being used now should still protect against severe illness, however.
What is the South Africa new variant?
All viruses, including the one that causes Covid-19, constantly mutate into new versions or variants.
These tiny genetic changes happen as the virus makes new copies of itself to spread and thrive.
Most are inconsequential, and a few can even be harmful to the virus's survival, but some variants can make the virus more infectious or threatening to the host - humans.
There are now many thousands of variants of the pandemic virus circulating. But experts are concerned about the South African variant, also known as 501.V2 or B.1.351.
Is it more dangerous?
There is no evidence that the South Africa variant causes 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.
But there are concerns it can spread more readily and vaccines may not work quite as well against it.
Some of the changes involve the virus's spike protein - the part that gains the virus entry into human cells. It is also the bit that vaccines are designed around, which is why experts are concerned about these particular mutations.
The South African variant carries a mutation, called N501Y, that appears to make it more contagious or easy to spread.
Another mutation, called E484K, could help the virus dodge a person's immune system and may affect how well coronavirus vaccines work.
Do vaccines work against the South Africa variant?
It is too soon to say for sure, or by how much, until more tests are completed, although it is extremely unlikely the mutations would render vaccines useless.
Scientists have tested the Pfizer Covid vaccine against N501Y and E484k mutations in the lab, using blood samples from vaccinated people.
In that study, vaccination appeared to work, but was slightly less effective.
Early results from Moderna suggest its vaccine is still effective against the South Africa variant, although the immune response may not be as strong or prolonged.
Preliminary work suggests the Oxford-AstraZeneca's vaccine offers "limited" protection against mild disease from the South Africa variant, but experts say it should still protect against severe disease.
Even in the worst case scenario, vaccines can be redesigned and tweaked to provide a better match in a matter or weeks or months, if necessary.
How far has it spread?
It is already the dominant virus variant in the Eastern and Western Cape provinces of South Africa.
At least 20 other countries including Austria, Norway and Japan, have also found cases.
In the UK, 188 cases of the variant have been found, with extra testing in the areas of England affected.
What is the UK doing about it?
Travel is now banned from many countries in southern Africa, as well as Tanzania and Democratic Republic of Congo.
Targeted testing in the community is also taking place in some parts of England.
Public health authorities and scientists are studying the variant and will share their findings soon.