Door to door coronavirus testing has begun in parts of England, after cases of the South African variant of Covid-19 were found unexpectedly.
Two cases of the variant were discovered in Surrey, and urgent testing is also taking place in London, Kent, Hertfordshire and Walsall.
The infected individuals had no known links to travel or previous cases, and were identified after random checks on tests by Public Health England.
What is the South African variant?
The South African variant is officially known as 501.V2. It is one of a few Covid-19 variants that have caught the attention of experts, after they caused an alarming increase in infections.
There is no evidence that the new variant causes much more serious illness for the vast majority of people who become infected. There are, however, concerns that it can spread more quickly, and that existing vaccines may not be quite as effective against it.
The variant carries a mutation of Covid-19 called E484K, among others. The mutation differs from the UK mutation found in Kent late last year. Both mutations were found to be more contagious.
While the UK variant is unlikely to harm the effectiveness of the Covid-19 vaccine, scientists have said there is a chance that the South African variant may alter the effectiveness to some extent.
A preliminary study testing the Pfizer Covid vaccine against one of the mutations found in the South African variant appeared to show the jab is effective against the mutated virus.
Early results from Moderna suggest that its vaccine is also still effective against the South African variant, however immune response may not be as strong or prolonged.
Vaccines can be redesigned and tweaked in a matter of weeks if necessary to tackle new variants.