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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 have warned after data revealed it was behind nearly one in 10 cases earlier this month.

The AY.4.2 strain was spotted in June by the Wellcome Sanger Institute, which sequences thousands of Covid samples in England every week.

And its prevalence has doubled in a month from causing four per cent of infections in September to 8.9 per cent in the two weeks to October 9.

Experts estimate that it could be up to 15 per cent more infectious than the original Delta strain, which is dominant worldwide. 

Some 45 different sub-lineages of the variant — which was first spotted in India — have been recorded so far. 

No10 is keeping a close eye on AY.4.2 but said there is ‘no evidence’ that it spreads more easily.

The graph shows the proportion of cases sequenced in England that are the new subvariant AY.4.2 (yellow) and Delta (blue). Delta became dominant in the UK in May, overtaking the previously dominant Alpha strain (purple)

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 sublineage 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.

How much more infectious is AY.4.2? 

How much more infectious is AY.4.2? 

Experts estimate the newly-emerged AY.4.2 subvariant is 10 to 15 per cent more transmissible that earlier version of the Delta strain.

Its prevalence in England doubled in a month from being behind four per cent of cases in September to 8.9 per cent in the two weeks to October 9.

But experts will need to keep monitoring the sublineage to determine if it really is more infectious.

Is AY.4.2 more deadly than earlier versions of Delta?

There is no evidence AY.4.2 is more deadly than earlier versions of the Delta strain, which was first identified in India last December.

Deaths in England have been relatively flat for months. 

Due to the time it takes for someone to catch the virus and become seriously unwell, any impact the subvariant has on deaths will likely not be clear for weeks.

Where has AY.4.2 been spotted?

The subvariant has been spotted in nearly every part of England. 

Data from the Sanger Institute, which sequences thousands of Covid samples in England every week, suggest 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).

The UK Health Security Agency 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 HSA said.

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

Data from the Sanger Institute suggest 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 Jeffrey Barrett, director of the Covid Genomics Initiative at the Sanger Institute, told the newspaper that AY.4.2 alone does not explain the the UK’s caseload, which is being linked to the UK imposing less restrictions than other countries. 

Official figures have shown cases are being fuelled by youngsters, with as many as one in 12 being infected.  

The Prime Minister’s official spokesman said ‘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 said 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.’


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