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23 June 2021updated 04 Oct 2023 9:55am

The “Delta plus” variant explained: what is the threat level?

Forty one cases of the mutant strain of Covid-19 have been detected in the UK, as concern rises in India about its impact.  

By Ido Vock

Indian scientists have classified a mutation of coronavirus related to the Delta variant, known as “Delta plus”, as a “variant of concern” (VoC). There were 155 confirmed cases of Delta plus, or AY.1, worldwide on 21 June, according to, a platform tracking data associated with the coronavirus pandemic. The variant has been detected in at least 11 countries, including the UK, where 41 cases have been identified so far.

According to India’s health ministry, studies show that the variant is more transmissible, more easily binds to human cells, and is potentially more resistant to antibody therapy – though more research will likely be needed before any of these characteristics can definitively be linked to Delta plus. Particular concern revolves around the mutation’s combination of the highly successful Delta variant with the K417N spike protein, which is found in the Beta variant first identified in South Africa.

Will Delta plus be designated a “variant of concern” by the World Health Organisation?

Coronavirus, like all viruses, mutates as it spreads. Delta plus is one of thousands of mutations detected during the pandemic, the vast majority of which are relatively inconsequential. But occasionally, mutations create variants that are more dangerous than previous versions, such as the four VoCs designated as such by the World Health Organisation (WHO). The Alpha variant, first detected in the UK, is believed to be about 40 to 80 per cent more transmissible than previous variants.

The Delta variant, believed to have originated in India, is thought to be around 60 per cent more transmissible again than the Alpha variant. Indian officials reportedly believe Delta plus may spread more easily than Delta, though information remains scarce and the number of confirmed cases relatively low.

Is the Delta plus variant more dangerous?

Scientists and officials have long feared that a variant could emerge that is immune to existing vaccines. Some press reports have speculated that Delta plus may be more easily able to escape antibody response triggered by previous infection or vaccination.

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The K417N mutation may allow the virus to more easily escape antibody protection, Charlotte Houldcroft, a researcher of virus evolution at the University of Cambridge, told me. “However, a lot of VoCs have this mutation too, suggesting scientists could rationally design a booster vaccine which would cover many variants at once,” she added.

Vaccines have been shown to work well on all existing VoCs, including Alpha and Delta, drastically reducing the likelihood of serious illness and death.

Are political factors at play in the response?

Whether the variant eventually becomes globally dominant will depend on several factors, including its ability to outcompete other variants and whether it can successfully evade immunity. However, most scientists believe that it is still too early to know whether that is likely to happen.

There could be other factors at play too in the response to the Delta plus variant so far, however. Jeremy Kamil, a virologist at Louisiana State University, told the BBC that the Indian government may be reacting especially strongly to Delta plus in order not to appear to have been taken by surprise if the variant does become established.

That would be in sharp contrast to its reaction to the emergence of the Delta variant, which caused a crippling second wave that killed up to 4,000 a day at its peak, according to official figures – which are themselves likely a significant underestimate.

[See also: Did Covid-19 escape from a Wuhan lab?]

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