What is the Delta variant and do Covid vaccines work against it?

A mobile Covid-19 vaccination centre outside Bolton Town Hall, Bolton, where case numbers of the Delta variant first identified in India have been relatively high.
A mobile Covid-19 vaccination centre outside Bolton Town Hall, Bolton, where case numbers of the Delta variant first identified in India have been relatively high.
Peter Byrne
Carl Bennett

By Carl Bennett


Published: 09/06/2021

- 15:44

Updated: 17/01/2024

- 13:32

The mutation that originated in India is now believed to be dominant in the UK

Public Health England (PHE) said early evidence suggests there may be an increased risk of hospital admission from the Covid-19 variant that originated in India.

The rise in hospital numbers comes as the new wave of Covid-19 infections continues to spread, driven by cases of the Delta variant.


Health Secretary Matt Hancock said the new strain Delta strain now accounts for more than 90% of cases in the UK.

Here's what you need to know about the Covid Delta strain.

Is the new strain more infectious?

The impact of the new variant has led to the average number of daily coronavirus cases rising, with the Reproduction (R) rate increasing to between 1 and 1.2.

PHE is investigating the variant “to better understand whether it could be more transmissible and less effectively tackled by vaccines”.

Professor Neil Ferguson, from Imperial College London, whose modelling was instrumental to the UK locking down in March 2020, said the Indian variant is anywhere between 30% and 100% more transmissible than the Kent variant.

New data from the PHE suggests people are more at risk of hospital admission if infected with the variant – although a majority of admissions involve those who have not been vaccinated.

Cases of the Delta variant are estimated to be doubling every four and a half days in parts of England, new data suggests.

More than 90% of new Covid-19 cases are now the Delta variant, with new research suggesting it is associated with an approximately 60% increased risk of household transmission compared with the Alpha or Kent strain.

Do Covid vaccines work against it?

Meaghan Kall, an epidemiologist at the PHE, said 73% of the cases involving the Indian variant are in unvaccinated people, while only 3.7% cases are in people who have had both doses.

A person receives a dose of the Pfizer BioNTech vaccine at a vaccination centre for those aged over 18 years old.
A person receives a dose of the Pfizer BioNTech vaccine at a vaccination centre for those aged over 18 years old.
Henry Nicholls

She said that only 5% hospital admissions were people who have been fully vaccinated, “suggesting that vaccination still appears to be making an impact on spread”.

Meanwhile, new laboratory data published on Thursday suggests that people who have received the Pfizer/BioNTech vaccine have fewer antibodies targeting the Indian variant – although real-world data is needed to confirm this.

Experts say that delivering second doses promptly and providing boosters to those with weakened immune systems will help keep hospital admissions low.

Dr Jenny Harries, chief executive of the UK Health Security Agency, said: “With numbers of Delta variant cases on the rise across the country, vaccination is our best defence.

“However, while vaccination reduces the risk of severe disease, it does not eliminate it.

“With data showing that Delta is significantly more transmissible than Alpha, it is just as important as ever to follow public health advice, which has not changed.

What are the Government doing to stop the spread?

Measures to try to halt the rise of the variant of coronavirus first identified in India will cover 10% of England’s population, as Health Secretary Matt Hancock said there was a “challenging decision” to be made over the further lifting of Covid restrictions later this month.

The Health Secretary announced on Tuesday that a “strengthened package of support” will be provided for Greater Manchester and Lancashire, similar to that seen in Bolton, where case numbers remain high.

Why was it renamed from the Indian variant?

Global health leaders announced in June new names for Covid-19 variants using letters of the Greek alphabet.

Experts working with the World Health Organisation (WHO) developed the labels for variants which are often colloquially named after the places where they are first detected.

The WHO said these labels were chosen after wide consultation and a review of many naming systems, adding that "calling variants by the places where they are detected" is "stigmatising and discriminatory."

Will Freedom Day be delayed?

Health Secretary Matt Hancock in Oxford
Health Secretary Matt Hancock in Oxford
Steve Parsons

A review of what measures will be relaxed on June 21 was due by the end of May but has been pushed back due to the Indian variant.

Downing Street has said plans for unlocking will be outlined on June 14.

The Health Secretary said the Indian variant had made the decisions behind the June 21 unlocking “more difficult” as he confirmed the latest advice is that the so-called Delta mutation is 40% more transmissible than the Kent variant.

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