It’s believed to have been responsible for close to 10% of all new infections at the start of October although it was first identified in July.
The UK Health Security Agency say it is only “expanding” and “on an increasing trajectory”.
Is this sub-variant more transmissible than Delta?
AY.4.2 has two mutations in it which could have strengthened the Covid strain’s transmissibility.
Scientists also believe the sub-variant is 10 to 15% more transmissible than the original Delta variant which has already dominated Covid cases around the world.
That would mean Delta Plus is be the most infectious variant to date.
But, according to the director of the Covid-19 Genomics Initiative at the Wellcome Sanger Institute Dr Jeffrey Barrett, this would “be annoying but not catastrophic” at the moment, as it may yet still die out.
Director of the Genetics Institute at University College London, Professor Francois Balloux, also pointed out that the sub-variant is not solely responsible for the recent infection spikes in the UK.
He said: “As AY.4.2 is still at fairly low frequency, a 10% increase in its transmissibility could have caused only a small number of additional cases.
“As such it hasn’t been driving the recent increase in case numbers in the UK.”
Some speculate that Delta Plus has the potential to become the more dominant strain in the UK but there is little evidence to support this theory yet.
So why is the sub-variant still concerning?
The variant itself is not necessarily that worrying at the moment, but it does demonstrate that Covid itself is continuing to evolve.
Dr Barrett explained on Twitter: “What is perhaps more worrying is that it suggests the virus still has evolutionary paths to higher transmissibility open to it, and there are millions of Delta cases around the world without much sequencing coverage.”
This means there is still space for Covid to continue adapting for further human transmission.
What has the government said?
The spokesperson for prime minister Boris Johnson explained that the government is keeping “a very close eye” on this particular sub-variant.
They added: “There’s no evidence to suggest that this variant, the AY.4.2 one, is more easily spread.
“But as you would expect, we’re monitoring it closely and won’t hesitate to take action if necessary.”
The strain is mainly dominant in the UK. Only three cases of the sub-variant have been detected in the States, with a handful of others in Denmark and Israel.
It would need to get a strong hold in several countries to avoid fizzling out.
Prof Balloux said: “This is not a situation comparable to the emergence of Alpha and Delta that were far more transmissible (50% or more) than any strain in circulation at the time.”
What does this mean for our fight against Covid?
Scientists are testing the new sub-variant to see if antibodies created by either natural immunity or vaccination are still effective against it or if it has immune evasion.
However, as the UK is experiencing a peak of Covid infections once again, there are concerns that this could be the perfect breeding ground for the new sub-variant.
Britain already has one of highest rates of infection in the world with the number of overall cases rising by 85% since the end of July.