A mutated form of Covid-19 may now account for up to one in four cases in parts of London, research shows.
Officials designated the strain AY.4.2, nicknamed Delta Plus, a ‘variant under investigation’ on October 20.
Scientists have said it may spread more easily than the standard Delta strain, but there is no evidence that it cause more serious illness.
There is also no evidence that the three Covid vaccines used in the UK are any less effective against the new strain.
Preliminary findings from the Wellcome Sanger Institute, one of the research bodies that works with the UK Health Security Agency (UKHSA), show potential hotspots for the new variant.
Its researchers analysed more than 26,000 positive Covid-19 tests from the week to October 30.
Southwark is London’s Delta Plus hotspot, with one in four Covid cases estimated to belong to the new strain.
Harrow has the second highest proportion of cases belonging to the new variant, at 24% of those tested.
Kensington and Chelsea has 18% estimated to be the new strain, while for Barking and Dagenham it is 17% of tests.
Bromley and Hillingdon both had 16% of sequenced tests belonging to Delta Plus.
Find out the situation in your borough using our interactive map below.
The research is provisional, but gives more localised detail than the official figures published by the UK Health Security Agency (UKHSA).
The UKHSA’s figures show Delta Plus accounted for 11.3% of cases in England in the week to October 24.
The South East has England’s highest rates of Delta Plus, accounting for 19.5% of cases on October 25.
Dr Jenny Harries, the agency’s chief executive, said: “Viruses mutate often and at random, and it is not unexpected that new variants will continue to arise as the pandemic goes on, particularly while the case rate remains high.
“It is testament to the diligence and scientific expertise of my colleagues at UKHSA, and the genomic sequencing capacity developed through the pandemic, that this new variant has been identified and analysed so quickly.
“However, it should serve as objective evidence that this pandemic is not over.
“The public health advice is the same for all current variants.
“Get vaccinated and, for those eligible, come forward for your third or booster dose as appropriate as soon as you are called.
“Continue to exercise caution. Wear a mask in crowded spaces and, when meeting people indoors, open windows and doors to ventilate the room.
“If you have symptoms take a PCR test and isolate at home until you receive a negative result.”