A new mutation of the Delta variant of COVID-19 is expanding in England and is being monitored and assessed, according to official UK health data reported on 19 October.

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AY.4.2, which is being dubbed as "Delta Plus" in some quarters, contains mutations that might give the coronavirus which causes COVID-19 a 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. 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 of 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," it said.