A new ‘Delta Plus’ variant has been detected in Britain and is responsible for a growing number of coronavirus infections.
The Delta variant - previously known as the Indian variant - is dominant in the UK but new data shows 6% of Covid cases genetically sequenced are of a new type.
Called AY.4.2, contains mutations that might give the virus survival advantages.
Tests are under way to understand how much of a threat it may pose but experts believe it is unlikely to take over and become dominant.
However Prof Francois Balloux, the director of the University College London Genetics Institute, suggests it could be 10% more infectious.
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.
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“As such it hasn’t been driving the recent increase in case numbers in the UK.
“The emergence of yet another more transmissible strain would be suboptimal.
“Though this is not a situation comparable to the emergence of Alpha and Delta that were far more transmissible at 50% or more.”
The UK is a global leader in carrying out genetic analysis of viral samples and has completed more than a million such tests looking for mutations.
The UK Health Security Agency announced on Tuesday that AY.4.2 is being monitored and assessed.
The next stage would be for it to be designated a ‘variant under investigation’ if there is a strong suggestion its mutations make it more contagious.
If it is shown to avoid immune protection built up from previous infection or vaccination it becomes a ‘variant of concern’.
Prof Balloux added: “The AY.4.2 is being closely monitored in the UK and elsewhere and remains rare outside the UK.
“There have been only three cases detected in the US so far. In Denmark, the other country that besides the UK has excellent genomic surveillance in place, it reached a 2% frequency but has gone down since.”
Downing Street insisted there was no evidence the variant spreads more easily.
Meanwhile Boris Johnson has insisted it’s not yet time for his Covid ‘Plan B’ in England despite rocketing cases and deaths.
A further 223 Covid deaths were recorded in the UK today - a seven-month high.
The Prime Minister’s official spokesman said there were “no plans” to use the contingency measures set out in the autumn/winter strategy.
“There are a number of different factors that would play into that decision,” the spokesman said.
“Largely it would be required when there was a significant risk of the NHS being overwhelmed.
“We are not at that point. Because of the vaccination programme, the levels we are seeing in both patients admitted to hospital and deaths are far lower than we saw in previous peaks.”
