A subvariant to the Covid Delta strain that is increasing in popularity in the UK is now being monitored by the World Health Organization. 

AY.4.2 — detected in all but 12 areas of England — is feared to be up to 15 per cent more infectious than its already highly virulent ancestor.

It was referred to by UK health officials as a “variant under investigation” last week. They are trying to determine how infectious it is and if it can evade vaccines better. 

The WHO is also paying special attention to AY.4.2 and has dedicated a whole segment of their weekly epidemiological report specifically to this strain.

The UN agency reported that more than 26,000 cases of the offshoot had been reported from 42 countries by October 25. 

The UK’s outbreak gets a special mention, given Britain — which has one of the strongest Covid surveillance schemes in the world — has detected around 93 per cent of the global total reported cases. 

The new Covid variant AY.4.2 has been found in 42 countries, but has been most prevalent in the UK, US, Denmark, Poland and Germany. This graph shows the percentage of AY.4.2 cases as a proportion of the country's total Covid cases. The UK has led case growth since the variant was fist identified in July, but in recent weeks Poland has eclipsed this, and there are signs Germany is also catching up

The new Covid variant AY.4.2 was found in 42 countries but is most common in the UK, USA, Denmark, Poland, Germany, and Poland. This graph shows the proportion of AY.4.2 cases to the country’s total Covid cases. Since July was the first time that the variant was identified, the UK has led in case growth. But, in recent weeks, Poland has eclipsed this figure and there are indications that Germany is also catching-up.

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 below shows 12 areas where AY.4.2 wasn’t detected in (white). This map was created between October 16th and October 16. It has spread rapidly to almost every part 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 stated that the slow rise was still compatible for a 10 percent transmission advantage over Delta.

It wants to know if the variant, which has been discovered in England, is any more dangerous than other strains.  

The WHO stated that there has been a ‘gradual rise’ in the proportion of AY.4.2 cases in Britain.

AY.4.2. Everything you need to Know 

Where did AY.4.2 come form?

According to UK-based tracking, this sub-variant was first identified in the UK on June 26.

Scientists believe that AY.4.2 developed in the UK because of its higher number of cases than other countries.

It is possible, however, that the variant was imported from overseas and spread throughout the country.   

Why is it limited to a few countries?

AY.4.2 has been spotted in over 40 countries, including the UK, Germany and Denmark.

It could have been missed in another location due to lack of Covid surveillance. This would result in new sub-variants not being spotted.

The slow spread may be due to travel restrictions, which make it less likely that the virus can be transmitted between countries.

How infectious is the Sub-variant?

Experts estimate that AY.4.2 may be around 10% more infectious than the Delta version.

They believe this will lead to a slightly higher number of cases, but not a spike comparable to that seen in the UK when Delta arrived. 

Do I have to be concerned about AY.4.2 

Scientists agree that there is no reason for concern about AY.4.2.

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

To assess this, lab tests are currently being performed at laboratories in the UK or Denmark. 

Professor Lawrence Young of Warwick University stated: “There is no reason that vaccines won’t work as well.”

Professor Anders Fomsgaard of Denmark’s Covid surveillance Centre said: “We are not concerned by that.” We don’t see anything that would indicate it is more contagious. 

Figures show that the new variant is responsible for approximately 10% of all new cases compared to 5% last month.  

The WHO report adds that further studies assessing if AY.4.2 is more contagious or deadlier are already underway. 

‘Epidemiological, laboratory and other studies are ongoing to determine if AY.4.2 confers any additional phenotypic effects (e.g. The report states that there was a change in transmissibility and a decrease of the ability of antibodies against the virus. 

The vast majority of the world’s samples for AY.4.2 have been collected in the UK, but there are signs that outbreaks could be occurring elsewhere. 

Britain’s top-ranked genomic capabilities make it better equipped to detect new strains even if they are from other countries. 

According to the latest surveillance data, AY.4.2 is responsible for around 16 percent of all Covid cases. 

But a lack of genomic Covid testing in Poland makes it hard to compare with Britain with the country only recording 132 cases of AY.4.2, compared to the UK’s 23,820. 

The UK’s Covid surveillance programs detected AY.4.2 in 315 of 315 local authorities in England during the fortnight ending on October 16.

Babergh and Burnley, Copeland and Hinckley and Bosworth, King’s Lynn, West Norfolk, Melton and Mid Suffolk, Newark, Sherwood, Oadby, Wigston, Pendle and Rushcliffe were the 12 areas where AY.4.2 wasn’t detected in the most recent fortnight. 

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 one in ten cases across the UK, slightly higher than one in 13 a fortnight back. But data also shows its curve is flattening.

Researchers at Northumbria University who are involved in variant surveillance claim that it is still ‘unclear” if AY.4.2 can be transmitted more easily because of the lack of information about its mutations.

As an alternative explanation, they suggested the ‘founder effect’, which is when a strain spreads quickly because it is the only one in a particular cluster of cases like a school. 

Professor Francois Baloux, a geneticist at University College London and Covid commentator, expressed concern about AY.4.2 last Thursday. He stated that the slower rise was’still compatible,’ with a 10 percent transmission advantage.

Professor Jeffrey Barrett, who runs Covid surveillance at Sanger Institute said that the data was consistent with a small but real growth advantage vs. other Deltas. 

AY.4.2 was first discovered in the UK in June. Since then, it has slowly spread throughout the country. 

It is not yet officially referred to, but it could soon be called “Nu variant” under the Greek alphabetical system used for naming new Covid viruses.


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 discovered in Spain on a variant (B.1.177). However, studies show that the strain was not more transmissible and was spread only by holidaymakers returning to their homeland.

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.