Only 12 areas in England have not yet reported a single case, experts fear, of an offshoot variant of the Delta Covid.

One of the largest Covid surveillance programs by the Government was detected AY.4.2 by 303 of 315 local authorities during the fortnight ending on October 16, the most recent available.

Babergh, Burnley and Copeland were the areas where AY.4.2 was missed in the most recent two weeks. 

Despite the fact that it is still outcompeting its ancestor’s data, scientists are now questioning whether the subtype is actually more transmissible than Delta.

Figures show that it is now behind 1 in 10 cases in the UK. This is slightly more than the one in 13 figures a fortnight earlier. However, the data also shows that its curve is flattening.

Scientists from Northumbria University are involved in variant surveillance. They say it is still unclear if AY.4.2 is more transmissible, as too little information is available about its mutations.

They suggested the ‘founder Effect’ as an alternative explanation. This is when a strain spreads rapidly if it is the only one among a specific group of cases, such as a school. 

Professor Francois Balloux at University College London, a geneticist, and Covid commentator, raised concerns about the variant last Wednesday. He said that the slower rise was’still compatible with’ a 10% transmission advantage.

Professor Jeffrey Barrett, who is responsible for Covid surveillance at Sanger Institute, stated that the data showed ‘consistently with a small but real growth advantage vs. other Delta’.

The above map shows the 12 areas AY.4.2 was not detected in (white) over the two weeks to October 16, the latest available. It has spread to almost every area of England

The map above shows the 12 areas where AY.4.2 was not found in (white) during the two weeks leading up to October 16, when the latest information became available. It has spread to almost all areas of England

The above chart showed AY.4.2 accounted for a slightly higher proportion of cases in the latest week ¿ one in ten ¿ compared to two weeks ago ¿ one in 13. Scientists said the slow rise was still compatible with a 10 per cent transmission advantage over Delta

The above chart showed AY.4.2 accounted for a slightly higher proportion of cases in the latest week — one in ten — compared to two weeks ago — one in 13. Scientists believe the slow rise is still compatible with a 10% transmission advantage over Delta.

The above map shows AY.4.2 cases across England over the two weeks to October 16. Darker colours suggest it is making up a higher proportion of cases, while lighter colours suggest it is making up a lower proportion of cases

The above map shows AY.4.2 case numbers in England during the two weeks up to October 16. It’s more common in darker colors, while it’s more common in lighter colours.

AY.4.2 first became known in the UK in June. It has since spread to other parts of the country. Experts believe it originated in London or the South East. However, there is no evidence to support this claim. 

It is a key mutation that carries two key mutations A222V or Y145H. These modifications slightly alter the shape and function of the spike protein the virus uses to invade cell cells.

Scientists claim that A222V was first seen on a variant (B.1.177), which was first discovered in Spain and then spread to other countries. However, studies show that the strain was not more transmissible and was spread only by holidaymakers returning to their homeland.

AY.4.2: All you need to know 

Where did AY.4.2 originate?

According to UK-based tracking, the sub-variant Delta was first discovered in the UK on June 26, 2012.

Scientists believe that AY.4.2 originated in the UK, as there are more cases than other countries.

However, it is possible that the variant imported from abroad was spread within the country.   

It is only available in a handful of countries.

AY.4.2 was spotted in more 40 countries to date, including the UK and Germany as well as Denmark and the USA.

It might not have been detected in other locations due to lack Covid surveillance. This could lead to new subvariants not being identified.

Travel restrictions could also be responsible for the slow spread of the virus, making it less likely that it will be transmitted between countries.

How infectious is the subvariant?

Experts believe that AY.4.2 is approximately 10 percent more infectious than the Delta-type variant.

They claim that this could lead to slightly higher numbers of cases but it won’t trigger a spike like that seen when Delta arrived to the UK. 

Do I have to be concerned about AY.4.2 

Scientists claim there is no reason not to be concerned about AY.4.2.

There is no evidence suggesting that vaccines are less effective against the subvariant or that it increases the likelihood of hospitalisation and death.

However, laboratory tests are being conducted in the UK and Denmark to confirm this. 

Professor Lawrence Young, Warwick University, stated that there is no reason for vaccines to not be as effective.

Professor Anders Fomsgaard, from Denmark’s Covid surveillance center, said that he was not concerned about this. We don’t see anything that would indicate it is more contagious. 

The mutation Y145H is a concern. It slightly alters how antibodies bind to the site, making it harder to stop an infection. 

Scientists believe this mutation is due to mutations in Delta and could make the subtype more resistant than its parent to vaccines.

AY.4.2 has been reported in more than 40 countries so far, but the UK is currently the only country experiencing a sustained outbreak.

In Denmark, it was at one in 50 Covid cases by September. However, it has fallen to one in 100 now. Experts in the nation say they are not concerned by AY.4.2.

It was last week referred to by UK health officials as a “variant under investigation”. This category is reserved to variants that are spreading in Britain and may be more transmissible than other mutant strains or better able of evading vaccines. It is one step below ‘variant-of-concern’, which includes Alpha. 

Scientists have questioned whether the AY.4.2 variant of Covid is actually more transmissible.

Dr Matthew Bashton, Dr Darren Smith, and both of them involved in Covid surveillance at Northumbria University have suggested that it might not be as transmissible.

In an article for scientific publication The Conversation, they wrote: ‘AY.4.2 has grown steadily in volume to the point where it now accounts for about nine per cent of UK cases in the last 28 days.

“But, whether its two mutations offer a virus a selective edge is also unclear.”

They concluded that it was too early to know if this is the beginning the next dominant lineage. Experimental work is required to confirm any ability it might have for escape immunity.

The scientists suggested the ‘founder effect’ may explain the spread of parent variant AY.4 — the most dominant Delta subtype which includes AY.4.2 — in the UK.

This happens when a ‘founder virus’ is the only one in an area where people mix, such as at a concert or school.

It spreads to the affected areas, resulting in a higher number cases than other mutant strains. This leads to data that suggests it is more easily transmitted, but in reality the increase could be due the events. 

The pair wrote: ‘Sometimes, for a certain form of a virus to dominate, it doesn’t have to be better than others — it simply needs to be in the right place at the right time.’ 

Professor Balloux stated that MailOnline had updated the Sanger Institute figures, which make up the bulk genomic surveillance in Britain. However, the variant was still around 10% more transmissible as Delta.

He stated that he felt that the most recent numbers were still compatible with a 10 percent higher transmissibility for A.4.2.

“If the lineage is at 1% on a given day it would be expected to rise to 11% five days later.”

Professor Barrett stated that ‘AY.4.2 continues slow rise in proportion: 9.7 percent in England in our latest two week average, just under 10 per cent if we only look at the most recently available week of data. 

“Another week consistent, but with small, but real growth advantage vs. the other Delta.”


The most recent technical briefing from the UK Health Security Agency — which replaced the now-defunct Public Health England — also suggested it may be more transmissible.

Scientists believe it has a modestly higher growth rate than the other variants and is more effective at spreading in households that Delta.

MailOnline was informed by Professor Lawrence Young of Warwick Medical School that although there isn’t any evidence of increased transmissibility, it’s still early days.

“We don’t know anything about AY.4.2’s immunology or whether it is more resistant than others to vaccine-induced immunity.”