AY.4.2, which is being dubbed as “Delta Plus” in some quarters, contains mutations that might give the coronavirus which causes Covid-19 greater survival advantage. The “sublineage” is increasing in frequency but experts do not believe it is responsible for the continued high number of daily coronavirus infections in the country, which hit 49,156 cases on Monday – the highest figure since July.

“New sublineages of Delta are regularly identified and designated. One recently designated sublineage is AY.4.2,” notes the UK Health Security Agency (HSA) in its latest technical briefing document.

“A Delta sublineage newly designated as AY.4.2 is noted to be expanding in England. It is now a signal in monitoring, and assessment has commenced; there are also small numbers of new cases of Delta with E484K and Delta with E484Q,” it adds.

The new mutation is not yet considered a variant of concern, or a variant under investigation – the categories assigned to variants and the level of risk associated with them. It was first noticed in July 2021 and since then this offshoot or sublineage of Delta has been slowly increasing. It includes some new mutations affecting the spike protein, which the virus uses to penetrate our cells.

“It is potentially a marginally more infectious strain,” Professor Francois Balloux, director of University College London’s Genetics Institute, told the BBC.

“It’s nothing compared with what we saw with Alpha and Delta, which were something like 50 to 60 per cent more transmissible. So we are talking about something quite subtle here and that is currently under investigation. It is likely to be up to 10 per cent more transmissible. It’s good that we are aware,” he said.

It comes as Downing Street said on Tuesday that it is keeping a “very close eye” at the rising number of daily coronavirus cases in the UK.

“We have seen case rates rising, we’ve started to see some indications that hospitalisations and death rates are increasing also,” the spokesperson for British Prime Minister Boris Johnson said.

“Clearly we’re keeping a very close eye on rising case rates, the most important message for the public to understand is the vital importance of the booster programme and indeed for those children who are eligible to come forward and get our jab,” the spokesperson said.

However, it said new infections were roughly in line with predictions and that the vaccine programme had “substantially” broken the link between cases, hospitalisations, and deaths.

On Monday, Britain reported 49,156 new Covid-19 cases and 45 more deaths within 28 days of a positive test, according to official data. This figure signifies a consistent 40,000 plus daily case numbers in the last week, with some experts warning a new peak of the disease may be around the corner in the country.

This story has been published from a wire agency feed without modifications to the text. Only the headline has been changed.