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Thousands of new cases of the so-called "Delta plus" coronavirus variant have been recorded in the UK in the past week.
Government figures published on Friday showed that 7,521 more people were infected with the AY4.2 variant in the week up to 27 October, the latest date for which data is available. This was second only to the original Delta variant which saw 57,411 new reported cases.
This brought the total of confirmed or probable cases of Delta plus to 28,667 across the UK, 21,158 of which were in England.
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The news strengthens suggestions that the strain is more transmissible than the original Delta variant from which it has mutated.
While the strain is currently still a VUI (Variant Under Investigation) there are fears it could become a Variant Of Concern (VOC) if rapid transmission continues.
This will be decided by an expert panel who investigate the transmissibility and strength of the strain, amongst other properties.
In contrast, an earlier VUI known as the Mu strain, has slowed to almost a stop in transmission, with just one new case recorded in the week.
The HSA has said AY4.2 does not appear to be causing more severe disease or render vaccines any less effective, however, work has already begun on a modified version of the Oxford vaccine to target the Delta coronavirus variant.
AY4.2 has been reported in 36 countries across the world, but the overwhelming majority have been identified in Britain.
The second worst-hit country is Germany with 379 cases, then Denmark with 304 and Poland with 159.
Experts have said that the variant's secondary attack rate – the probability of an infection occurring in a group of people – is around 12.4 per cent for a household in the UK, while it is 11.1 per cent for the Delta variant, meaning there is a greater chance of infection spreading within a household if one person is infected with Delta plus.
The overall number of COVID cases in the UK remains high, and on Thursday there were 36,559 new infections reported, meaning rates of infection are similar to those during the January peak.
However, hospitalisations and deaths due to COVID-19 are much lower than during the second wave last winter.
There was further good news this week when the first anti-viral pill for Covid-19 that can be taken at home was approved for use in the UK.
It is hoped molnupiravir could cut the rate of hospital admission and death by 50% in mild-to-moderately ill patients.
Researchers behind the Zoe COVID Study from King’s College London said on Friday that on average one in 53 people in the UK currently have symptomatic COVID and the number of daily new cases is showing a clear decline among those aged 18 and under, with most other age groups showing signs of levelling off.
Professor Tim Spector, the lead scientist on the study, said: "It’s great that we’re finally seeing cases start to come down, and hopefully we’re over the last great peak of COVID in 2021.
"This is driven in large part by declining cases in children who have been on half-term holidays and by high rates of previous infection, but we’re hopeful that the trend will continue."
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