A “DELTA” plus variant is spreading into more countries and is being carefully monitored by scientists.
Its significance, and whether it is more dangerous than previous variants, is not yet clear.
What makes it concerning is that it is the Delta variant, which has swept the globe, with additional features.
Delta is highly contagious and is causing new challenges for places like the US and China – where cases are reaching new record levels despite vaccine efforts.
Reports of Delta plus cases have been in a handful of countries, including the UK, USA, Portugal, India, Nepal, China and most recently South Korea.
But cases have not taken off. They appear to mostly be in younger people, which may be as a result of lower vaccine rates.
Scientists are racing to understand more about this strain.
Here is everything we know about the variant so far.
What is the Delta plus variant?
The Delta plus variant has a scientific name of AY.1.
It has the same mutations as the Delta variant, first seen in India and now dominant globally, “plus” the addition of one more mutation – K417N.
This has been seen in other variants, including that from South Africa (Beta) and Brazil (Gamma).
It has not yet been given an official name by the World Health Organization (WHO) but comes under the Delta “variant of concern” bracket.
India has classified Delta plus as a “variant of concern” because health officials said it appeared to be better at binding to lung cells and evade Covid treatments.
But experts were wary, with Dr Gagandeep Kang, a virologist and the first Indian woman to be elected Fellow of the Royal Society of London, telling the BBC “there is not date yet to support” Delta plus was a concern.
Does it spread faster and will vaccines work against it?
Delta plus has the same components as Delta, suggesting it would behave in the same way – although this is not clear.
The Delta variant is fast-spreading – up to 50 per cent more than the Alpha/Kent variant – and so Delta plus is possibly just as contagious.
It can also evade some vaccine protection, with one dose of either Pfizer or AstraZeneca giving just 33 per cent protection.
Meanwhile, the additional K417N mutation “is believed to be part of why the Beta variant is less well neutralised by vaccines”, Dr Jeff Barrett, Director of the COVID-19 Genomics Initiative at the Wellcome Sanger Institute, said in June.
But K417N is not thought to contribute to faster spread.
Francois Balloux, professor of computational systems biology and Director, UCL Genetics Institute, UCL, said: “The K417N mutation has arisen independently in several viral lineages.
“None of the lineages carrying it (with the exception of Beta) have been particularly successful so far.”
Delta plus in itself has not been studied very intensively.
Studies are ongoing in India and globally to test the effectiveness of vaccines against this mutation.
Prof Balloux said: “Given the tiny number of strains reported, nothing is known about the transmissibility, immune evasion or lethality of the Delta plus strain.
“Though, given that it has remained at very low frequency everywhere where it has been identified strongly suggests it is not more transmissible than its Delta progenitor.”
Ravi Gupta, Professor of Clinical Microbiology, University of Cambridge, added: “As yet there is no clear evidence that the AY.1 is more transmissible or immune evasive than the Delta variant.”
How many cases are there?
There have been 52 cases detected in the UK as of July 31, after arriving on April 28.
Only four of these were in the past 28 days, suggesting it has not spread very far.
Most of the cases have been in England (46), followed by Wales (3), Scotland (2) and Northern Ireland (1), according to the COVID-19 Genomics UK Consortium.
What are the symptoms?
There is no indication the variant linked to Nepal has any new symptoms.
The key symptoms to look out for with Covid infection are loss of taste and smell, a new continuous cough and a high temperature.
But doctors say if you feel unwell at all, you should get a Covid test anyway.
More common symptoms, according to the Zoe Covid Symptom study app, are headaches, fatigue, runny nose and sore throat, as well as sneezing in vaccinated people.
Should we be worried?
New variants are constantly arising and will continue to do so.
They become a threat when they contain mutations that could significantly weaken vaccines, or are so transmissible that usual measures don’t work to contain it.
At this stage, it is not clear how dangerous the Delta plus variant is.
Prof Balloux said: “At this stage there is no particular cause for concern.
“It has been found in several countries but has remained at extremely low frequency, with the exception of Nepal where it has been estimated at ~4 per cent (but based on a tiny sample size 3/70).
“Delta+ represents 0.00002 per cent of all Delta variants sequenced to date. There is no evidence the strain is currently expanding in any country.”
Is the Delta plus variant the same as the Nepal variant?
Delta plus originally went by the name of the “Nepal variant”, because it had been seen there most commonly.
It first made headlines in June when the British Government put Portugal on the amber list because it was concerned the country had detected the variant.
World Health Organization Nepal said it had not been aware of a new variant from the country.