A new sub-strain of Delta has been identified and it contains an extra spike mutation that may make it easier for the virus to infect individuals. The Delta Plus variant has been found in at least 44 countries and 41 US states, according to outbreak.info, which compiles data from the GISAID COVID tracking initiative.


The altered variant was confirmed to be in the UK in April 2021, and data reported by Public Health England (PHE) on 26 November 2021 shows that there have been a total of 421 Delta Plus cases so far.

More research is needed before we can say exactly how Delta Plus will impact the UK, but early studies suggest the mutation will not be able to evade the protection offered by vaccines.

One pre-print study, which is yet to be peer-reviewed, of Delta Plus suggests that the effect of the Pfizer vaccine is "only modestly reduced" against the new strain, when compared with the original SARS-CoV-2 virus.

The Delta Plus variant was classified as a variant of concern by Indian health officials, but PHE and the World Health Organization (WHO) continue to categorise Delta Plus within figures for the Delta strain.

It is believed to have originated in India, where the Delta strain was first found. In June 2021, the BBC reported that India's health ministry claimed studies showed Delta Plus spreads more easily, binds more easily to lung cells and is potentially resistant to a type of COVID-19 treatment called monoclonal antibody therapy.

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But Professor Ravindra Gupta, an expert in infection and immunity at University of Cambridge, told BBC Science Focus magazine that Delta Plus was unlikely to cause more severe illness.

"[Delta Plus] has a change called K417N as its key mutation," explained Gupta. "Delta doesn't have this mutation, but variants of Delta have been expected to arrive."

Gupta explains that scientists are not surprised to see mutations that slightly reduce the effectiveness of antibodies, which are the body's main line of defence against viruses. These antibodies are created when a coronavirus vaccine is administered, or produced naturally after infection with any COVID-19 strain.

"The virus is circulating now in populations that already have a bit of immunity. So, they will be picking up mutations that enable additional escape [from that immunity] or reduce susceptibility to vaccines.

"But on the other hand, we are covered by broad responses when we get vaccinated or and have boosters, so I don't think these mutations are going to significantly knock off the protective effect of vaccine against severe disease."

How is the Delta Plus strain different to Delta?

Delta Plus refers to sub-strain of Delta that has a mutation on what is called K417N. This mutation is found in two versions, Delta AY.1 and AY.2, which are both referred to as Delta Plus.

The mutation affects an area of the spike protein called the receptor-binding domain. This area is what governs how effectively the virus can attach onto cells, and K417N is thought to help the virus create a stronger binding between itself and its host.

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This could make it easier for the virus to infect individuals. However, PHE has said that very preliminary results for live virus neutralisation from vaccines are reassuring.

A map of occurrences of the AY.1 Delta Plus variant of coronavirus, as of 29 September 2021 © cov-lineages.org
A map of occurrences of the AY.1 Delta Plus variant of coronavirus, as of 29 September 2021 © cov-lineages.org

Delta Plus is not the only strain with the K417N mutation.

"We saw the this mutation come on top of the Alpha strain," explains Gupta. "But it never really took over the original Alpha. So I think that single mutations on top of variants aren't really going to give it a huge advantage over the original."

But some researchers have warned against focusing only on the K417N spike in Delta Plus.

"The Delta Plus variant had a significant number of high-prevalence mutations than in the Delta variant," they write in their paper, published in the Journal of Autoimmunity. "Three mutations were exclusively present in the Delta Plus variant, while five key mutations were significantly more prevalent in the Delta Plus than in the Delta variant.

"Based on the results presented here, it is clear that the Delta and Delta Plus variants have unique mutation profiles, and the Delta Plus variant is not just a simple addition of K417N to the Delta variant."

How many cases of the Delta Plus variant have been detected in the UK?

The UK Government is not counting Delta Plus as a separate variant, which means the figures are included in reports about the original Delta strain.

The latest figures, reported on 26 November 2021, show there have been a total of 1,370,519 Delta cases in the UK, of which 421 were Delta Plus. In comparison with the figures reported 17 November, it appears there have been 48 new Delta Plus cases across that seven day period.

What are the symptoms of the Delta Plus variant?

At present, there is nothing to suggest that the symptoms of infection with the Delta Plus variant are different to other coronavirus strains.

The main symptoms of COVID-19, according to the NHS, are:

  • a high temperature – this means you feel hot to touch on your chest or back (you do not need to measure your temperature)
  • a new, continuous cough – this means coughing a lot for more than an hour, or three or more coughing episodes in 24 hours (if you usually have a cough, it may be worse than usual)
  • a loss or change to your sense of smell or taste – this means you’ve noticed you cannot smell or taste anything, or things smell or taste different to normal

The NHS say that most people who have symptoms of COVID-19 will have at least one of the above.

Will vaccines still work against the Delta Plus variant?

While it is too early to conclusively say whether vaccines will be affected by Delta Plus, initial studies suggest the K417N mutation is unlikely to have a big impact.

In the pre-print study that tested the Pfizer vaccine against Delta Plus, scientists said it appeared the mutation "has not led to virus escape from vaccine-elicited neutralising antibodies".

Gupta, who was not involved in the Pfizer study, says that there is a rationale for developing Delta-specific vaccines.

"Existing vaccines appear to be protecting many people from severe disease. But you need much higher levels of antibodies to protect against Delta than you do for the original virus strain, and so Delta-specific vaccines are desirable."

What other variants of concern have been identified in the UK?

It is common for viruses to mutate when they replicate. Few of these small, genetic changes lead to a more harmful infection.

As of 26 November 2021, there are four strains considered to be ‘of concern’ by PHE, including the Delta and Alpha variants.


The PHE are monitoring a total of 15 variants.

About our expert, Professor Ravindra Gupta

Professor Ravindra Gupta leads the Gupta lab at the University of Cambridge, where he works on the genetics and biology of HIV resistance.

During the COVID-19 pandemc, the Gupta lab has studied several aspects of the virus, including the effect of antibody-based therapies and the emergence of new variants and how they impact natural and vaccine induced immunity.


Amy ArthurEditorial Assistant, BBC Science Focus

Amy is the Editorial Assistant at BBC Science Focus. Her BA degree specialised in science publishing and she has been working as a journalist since graduating in 2018. In 2020, Amy was named Editorial Assistant of the Year by the British Society of Magazine Editors. She looks after all things books, culture and media. Her interests range from natural history and wildlife, to women in STEM and accessibility tech.