COVID: 'Slowly' increasing numbers of Delta 'AY4.2' variant investigated by health bosses

·3 min read
Covid-19 variant of concern public health NHS advertising board with just five more days to the official 'freedom day' planned for the 19th July, people, many of whom are wearing face masks, come to the city centre retail shopping district on 14th July 2021 in Birmingham, United Kingdom. After months of lockdown, but with case numbers rising, in particular that of the Delta Variant, there is hope that life will start to return to normal, with restrictions like the compulsory wearing of face coverings in public spaces ending. (photo by Mike Kemp/In Pictures via Getty Images)
Health bosses are investigating a new COVID-19 variant labelled the 'Delta plus' (Mike Kemp/In Pictures via Getty Images)

The numbers of a new variant of the Delta strain of COVID-19 are rising in the UK, new data has revealed.

AY4.2 is a sub-lineage of the Delta variant and some experts fear that this “Delta plus” variant, as it has been labelled, appears to be more transmissible.

Government figures published on Friday said that AY4.2 cases account for a "slowly increasing proportion of cases in the UK".

The data shows AY4.2 accounted for 8.5% of Delta cases in the week ending 10 October. Preliminary analysis suggests this could have risen to 10.3% of all Delta cases for the following week and 11.3% the week ending 24 October.

Critically, initial analysis does not suggest the new variant causes a "significant reduction" in vaccine effectiveness. However, health chiefs are carrying out more comprehensive testing to confirm.

The Health Security Agency (HSA) moved the AY4.2 into the category of Variant Under Investigation (VUI) on 21 October, adding that it was “expanding” and “on an increasing trajectory”.

As a VUI the strain will undergo a risk assessment with the relevant expert committee, after which it could be designated Variant of Concern (VOC).

People wearing face masks among crowds of pedestrians in Covent Garden, London. Rumours were abound in the Sunday newspapers that Prime Minister Boris Johnson, who is due to update the nation this week on plans for unlocking, is due to scrap social distancing and mask-wearing requirements on so-called
As cornavirus cases rise in the UK, heath experts are investigating new variants (Dominic Lipinski/PA Images via Getty Images)

The AY4.2 strain has been detected in 33 countries across the world, but the overwhelming majority of cases are in the UK, according to, a website that documents the lineages of the virus.

Denmark, Germany and Ireland have also reported cases of the Delta plus as well as the US, Israel, Russia and India.

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.

The number of coronavirus cases has been creeping up since August and has reached around 39,000 new cases each day (JHU COVID data)
The number of coronavirus cases has been creeping up since August and has reached around 39,000 new cases each day (JHU COVID data)

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 UK has experienced a marked rise in COVID cases in the past few weeks, though that increase has tapered off in recent days.

On October 23 there were 44,985 new cases recorded in one day, the highest figure since the January peak, but on Thursday the number had dropped slightly to 39,0006.

On Thursday, Sir Patrick Vallance said that waning immunity and the public's behaviour will be the main factors that determine whether the UK sees further spikes in cases of COVID.

“Nobody is really clear which direction this is going in, but they are clear about the two big variables that could change that," he told BBC Breakfast.

“One is waning immunity; so if immunity wanes faster than expected, you’ll see a bigger increase, and that’s why it’s so important to get booster shots going in the vulnerable and the elderly in particular.

“The second is the behavioural change, how quickly we return to pre-pandemic behaviours… if you aggregate the models, most are saying: ‘Actually, it looks fairly flat, don’t expect the very big peaks we’ve had in the past, it looks fairly flat, but at a very high level at the moment.’

“So, the high level remains a concern and from a high level you can go up quite quickly.”

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