Is an even MORE infectious strain of Delta now taking off in Britain?

A subvariant of the Covid Delta strain could be more infectious than its ancestor, experts warned today after data revealed the proportion of cases linked to the strain has doubled in a month.

AY.4.2, as it is currently known to scientists, made up almost 10 per cent of all infections in England in the fortnight ending October 9. Virus-trackers at the Wellcome Sanger Institute, which sequences thousands of Covid samples every week, say its prevalence stood at just four per cent in mid-September. 

Academics estimate it may be up to 15 per cent more transmissible than the original Delta, which rapidly became dominant in Britain in the spring before taking off worldwide. 

It has been detected in almost every part of the country, figures show, and it’s thought to be behind almost 60 per cent of positive tests sampled sequenced in Adur, West Sussex. 

No10 today said it was ‘keeping a very close eye’ on AY.4.2 but insisted there is ‘no evidence’ that it spreads easier. Boris Johnson’s official spokesperson also warned the Government ‘won’t hesitate to take action if necessary’.

The warning comes as Covid cases continue to spiral across the UK, with daily infections yesterday shooting up to almost 50,000 in a three-month high. 

Experts suggested the uptick of AY.4.2 — one of 45 sub-lineages of Delta — may be partly to blame, along with the return of pupils to classrooms from August and workers to offices. 

SAGE fears there will be a fourth wave by the end of the year that may cripple the NHS. Ministers are overseeing a rollout of booster jabs to over-50s, healthcare workers and the immunosuppressed to protect the health service as much as possible.

But experts have warned the top-up jabs are being dished out too slowly, with 5million vulnerable adults eligible for a third dose yet to receive one. 

Influential Government adviser Professor Neil Ferguson, an epidemiologist at Imperial College London, today insisted it was ‘critical we accelerate’ the booster drive to give ourselves the best chance of avoiding having to bring back curbs.

In other Covid developments today:

• Nearly 5million vulnerable adults have yet to have their Covid booster vaccine, official figures show;
• ‘Professor Lockdown’ Neil Ferguson says it’s ‘critical we accelerate’ the booster drive with fears growing over s ‘challenging’ winter which could see return of face masks and work from home guidance;
• Professor Ferguson also called for return of face masks and for teenagers to get two Covid vaccines;
• The head of the NHS said the health service was never overwhelmed by Covid during the height of the pandemic;
• Amanda Pritchard also warned MPs pressures on the health service could see thousands more hospital treatments cancelled;
• Her comments were echoed by Health Secretary Sajid Javid, who told MPs there is ‘huge pressure’ on the health service in England. 

Professor Francois Balloux, director of the University College London Genetics Institute, told the Financial Times the strain could be the most infectious subvariant seen since the pandemic began.

But he noted Britain is the only country where the sub-lineage has ‘taken off’, so its quick growth could be a ‘chance demographic event’.

The World Health Organization will likely elevate AY.4.2 to a ‘variant under investigation’, which means it would be given a name under its Greek letter naming system, Professor Balloux added. 

He said: ‘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 — 50 per cent or more — than any strain in circulation at the time. 

‘Here we are dealing with a potential small increase in transmissibility that would not have a comparable impact on the pandemic.’

The UK Health Security Agency, which took over from the now-defunct PHE, revealed in a report on Friday that the subvariant is expanding in England. 

It includes two mutations — called Y145H and A222V — and is being monitored, the UKHSA said.

Both of these spike mutations have been found in other virus lineages since the pandemic began — but are not present on any current variant of concern. 

Professor Balloux said the mutations are not obviously linked with increased transmissibility or evading protection granted by vaccines.

Only three AY.4.2 cases have been spotted in the US, while two per cent of cases in Denmark are caused by the sub-lineage, he added.

Data from the Sanger Institute suggests the sub-lineage is most prevalent in Adur, where 61 per cent of all positive samples sequenced were linked with AY.4.2.

The subvariant also seems to be highly prevalent in East Lindsey (46 per cent) and Torridge (41 per cent).

It comes as the UK recorded 49,156 new Covid infections yesterday, marking another three-month high. Hospitalisations and deaths are also on the rise. 

Some experts have said the subvariant may be behind the surge, which other European countries are not seeing to the same extent. 

Former US Food and Drug Administration commissioner Scott Gottlieb tweeted on Sunday: ‘We need urgent research to figure out if this “delta plus” is more transmissible, has partial immune evasion.’

But Dr Jeffrey Barrett, director of the Covid Genomics Initiative at the Sanger Institute, told the Financial Times AY.4.2 alone does not explain the the UK’s caseload, which is instead linked to the UK imposing less restrictions than other countries. 

Professor Balloux said its rapid spread ‘could have caused a small number of additional cases’, but added: ‘It hasn’t been driving the recent increase in case numbers in the UK.’

Official figures have shown cases are also being fuelled by youngsters returning to classrooms last month, with as many as one in 12 being infected.

The Prime Minister’s official spokesman said the Government is ‘keeping a very close eye on’ the subvariant.

They said: ‘There’s no evidence to suggest that this variant … the AY.4.2 one … is more easily spread. There’s no evidence for that but as you would expect we’re monitoring it closely and won’t hesitate to take action if necessary.’ 

Dr Alexander Edwards, an immunologist at the University of Reading, told MailOnline it would be concerning if a variant starts to dominant that evades vaccine immunity. 

He said: ‘Before the successful rollout of vaccines, this was less likely to happen, but now, with such a high proportion of the population infected, alongside waning immunity, now is the time to be extra vigilant.  

‘Luckily, we can redesign our vaccines very quickly now, so there isn’t yet anything to be afraid of. 

‘But any efforts made now to reduce cases and improve immunity — through boosters, vaccinating younger people, testing and effective isolating — could pay off if they cut the risk of vaccine evading variants.’ 

Professor Lawrence Young, a virologist at the University of Warwick, told MailOnline the detection of AY.4.2 ‘highlights the need for continued genomic surveillance of the virus’. 

Experts will need to monitor it to determine ‘if it really is more transmissible and if it has any impact of the efficacy of vaccination’, he said.

Professor Young added: ‘The continued spread of the virus at a high level in the UK increases the risk of variants being generated that could be more infectiousness and more able to evade vaccine-induced immunity.’

It comes as official figures show nearly 5million vulnerable adults have yet to receive a Covid booster vaccine, after Downing Street admitted Britain faces a ‘challenging’ winter.

Despite the NHS top-up programme launching over a month ago, only around 3.7million out of the 8.5m eligible people in England have received the crucial third dose.

No10’s scientists approved plans to revaccinate all healthy over-50s, frontline health staff and carers and patients with underlying medical conditions six months after their second dose, after evidence showed it was the ‘sweet spot’ for immunity. 

The lagging rollout has left around 4.8m people with sub-optimal immunity as the country moves into the colder months and faces the double threat of increasing case numbers and flu.

SAGE adviser ‘Professor Lockdown’ Neil Ferguson, an epidemiologist at Imperial College London, today insisted it was ‘critical we accelerate’ the booster drive to give ourselves the best chance of avoiding having to bring back curbs.

And Sir David King, who was the Government’s chief scientific adviser from 2000 to 2007, criticised the rollout for moving ‘extremely slowly’.

Amanda Pritchard, chief executive of the NHS, insisted the health service has ‘plenty of capacity’ to vaccinate all eligible people immediately but said people are not coming forward quickly enough. She told MPs on the Health Committee: ‘It’s really important that we now absolutely do get the message out that is Covid is still with us.’

But some experts also say the booster programme is going slower because the UK is juggling administering first jabs to children in secondary schools and running the largest flu vaccination programme in history. 

Pictures today show clinics lying virtually empty, some of which are not open for booster jab walk-ins — further highlighting the complexity of Britain’s current rollout.

It comes against the backdrop of rising cases with 49,156 infections recorded yesterday — the highest daily figure in three months. Downing Street warned that Britons should prepare for a ‘challenging few months’ 

 Boris Johnson’s spokesman said there were ‘currently’ no plans to reintroduce Plan B restrictions — which include face masks and working from home guidance — but that ministers were keeping ‘a very close watch on the latest statistics’.

Britain led the world in the initial vaccine rollout, but it has now slumped behind Italy, Spain and France in terms of the percentage of the population to be double-jabbed. 

This is because it delayed rolling out jabs to healthy children, whereas most EU members approved those plans much quicker.

All over-50s and the clinically vulnerable can get a booster jab from six months after their second dose. 

But experts have warned that at the current rate the most vulnerable will not all receive their third vaccination until the end of January.

Asked if Covid booster jabs are the answer to waning immunity, Professor Ferguson told BBC Radio 4’s Today programme: ‘Absolutely, and there’s data coming through now, which is not completely clear cut, but good data coming through from Israel, which shows that, if you’ve had the third booster dose of the vaccine, then you get very high loads, better than even you had after the second dose.

‘And so I do think it’s critical we accelerate the booster programme.

‘The other thing is infection rates are highest in teenagers at the moment and most other European countries are ahead of us in vaccinating teenagers and giving them two doses, not just one dose.

‘Two doses really are needed to block infection and prevent transmission, so I think that’s the other problem, keep pushing on, getting coverage rates up higher in the teenagers who are driving a lot of this infection.’   

He also called for face coverings to be brought back to remind people to be cautious in everyday interactions and ‘remind people we’re not completely out of the woods yet’.

All legal Covid restrictions were lifted in England on ‘Freedom Day’ in July, bringing an end to mandatory coverings indoors. However, people are still required by some transport companies and in medical settings — and No10 still advises people wear them in crowded environments.  

Ministers are keeping masks, WFH guidance and controversial vaccine passports in their back pocket as part of the Government’s ‘Plan B’, if an expected surge in cases this winter heaps unsustainable pressure on the NHS. 

Professor Ferguson, an epidemiologist who sits on SAGE, admitted some measures have to be rolled back, in the event of an uptick in infections. 

But speaking to BBC Radio 4’s Today programme, he ruled out another blanket shut-down. He said: ‘I doubt we’ll ever get close to [the] lockdown we were in in January of this year.’