A subvariant of the Delta strain of Covid-19, the more transmissible mutation of the coronavirus now in widespread circulation, is under investigation.

But the fact that it has not officially been given a letter of the Greek alphabet of its own is a sign that it just being watched for now.

What is the 'Delta Plus' variant?
The variant, known by its scientific identity AY.4.2, is a relative of the Delta variant, also known as B.1.617.2 and first identified in India last October. Delta is now the dominant strain globally. The subvariant has new mutations in the spike protein, helping the virus invade the body's cells.

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Is it a more dangerous version of the virus?
There is no evidence to suggest that it causes more severe illness or greater mortality than the Delta variant or that it can escape the protection afforded by Covid-19 vaccines but scientists think that it might be more contagious, helping the virus spread more easily than earlier versions.

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So how transmissible could it be?
Two scientific experts – Jeffrey Barrett, director of the Covid-19 Genomics Initiative at the Wellcome Sanger Institute in Cambridge, and Francois Balloux, director of the University College London Genetics Institute – have said that it seems to be 10 to 15 per cent more transmissible than the original Delta variant. Early evidence suggests it has increased the growth rate in the UK.

How does that compare with past variants?
The Delta variant was 60 per cent more transmissible than the Alpha variant first identified in the UK in the second half of 2020 that caused Ireland's third and worst wave of the pandemic. Alpha was itself 50 per cent more transmissible than the original virus that spread from China.

Are scientists concerned?
It is more a case of watching anxiously rather than being actively concerned. The UK Health Security Agency has moved the 'Delta Plus' variant into "variant under investigation" category but it is not yet considered a "variant of concern", the highest risk category for variants which would result in Delta Plus receiving its own letter of the Greek alphabet. Scientists are still checking evidence to see how AY.4.2 is behaving and whether it should be a cause of concern. Viruses evolve naturally and the AY.4.2 is one of 45 "sub-lineages" descended from the Delta variant.

Could it take off?
The scientists who have investigated the strain say that it presents nothing like the challenge posed by the Alpha and Delta variants because the increase in transmissibility is not of the same scale and a small rise in transmissibility would not change the nature of the pandemic.

Where is the 'Delta Plus' variant?
Most cases appear to be in the UK but it is still the minority variant there. A small number of cases have been reported in Denmark, Germany, the US, Israel and Russia. Cases of the variant have actually fallen in Denmark. The UK is the only country where it has risen in frequency, accounting for 6 per cent of all strains sequenced where the make-up of the virus is identified.

Have any cases been detected in Ireland?
Yes, Dr Cillian De Gascun, the director of UCD's National Virus Reference Laboratory, has said that more than 80 cases have been identified here in sequencing. The variant is still rare: in September, it accounted for less than 2 per cent of more than 4,000 Covid-19 cases checked.

What more is being done about it here?
Dr De Gascun said that the laboratory will go back and investigate the 'Delta Plus' cases to see where they were in the country and what age groups the variant infected – and whether the variant led to more severe disease in the people affected. The objective of the investigation is to tease out more about how the sub variant is behaving. That exercise is likely to take a few weeks.