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The Delta variant of coronavirus: 4 key questions

The science that's behind a very big decision

Could B.1.617.2 threaten the proposed end of lockdown in England on 21 June? Dr Elizabeth Webb answers this and other pressing questions about 'the Delta variant'.



Update - Monday 14 June

Please note: this article has been updated to reflect the name of the variant of coronavirus first found in India. 

There's been a lot of speculation around B.1.617.2, the COVID strain first detected in India commonly known as 'the Delta variant'. Does it spread more quickly? Is the vaccine effective against it? Will it delay the proposed end of lockdown on 21 June? Dr Elizabeth Webb explains what we currently know, and the factors the Government will be weighing up. 

The key criteria

In February the Government outlined 4 ‘tests’ they would use to determine whether each step of the easing of restrictions should go ahead. These were:

  • the vaccination programme continues successfully
  • hospitalisations and deaths are reduced in vaccinated people
  • infection rates aren’t risking a surge in hospitalisations
  • risks are not fundamentally changed by Variants of Concern

Throughout the easing of restrictions, the first 3 tests have been comfortably met. More than half the UK population has now had at least 1 vaccine dose and Public Health England estimated that vaccinations had prevented 33,000 hospitalisations and 11,700 deaths by the end of April. Infection rates are low with fewer than 1 in 1,000 people having coronavirus and numbers of people in hospital have fallen to the relatively low levels last seen in summer 2020.

However, the impact of the most recent easing of restrictions – on Monday 17 May, when indoor hospitality opened – on infections and hospitalisations is not yet certain.

The fourth test has caused more concern. Since last autumn, some key variants of concern have been detected in the UK. First, the UK or Kent variant (B.1.1.7) then the South African and Brazilian variants (B.1.351 and P.1, respectively). The Kent variant is now the most common variant in the UK and is spreading around the world. The South African and Brazilian variants have not become widespread in the UK.

More recently, we have heard about the Delta variant (B.1.617.2), of which there have now been more than 3,400 cases confirmed in the UK, concentrated mainly in areas of the North West of England, as well as the East Midlands and London, but now identified in many areas.

There are 4 key questions to ask about the Delta variant:

1. Is it easier to catch?

It’s difficult to work out whether B.1.617.2 is easier to catch than other coronavirus variants, however evidence increasingly suggests that it is. Estimates suggest that it may be between 10% and 50% more transmissible than the Kent variant.

2. Does it make people more unwell?

There is no evidence to suggest that B.1.617.2 makes people who catch it more unwell or increases the chances of hospitalisation or dying than previous variants of coronavirus. However, as the numbers of people with B.1.617.2 are still relatively small and most cases are quite recent, it is too early to know with certainty.

3. Will the vaccines protect us?

Early evidence suggests that the vaccines we have will protect us, but that the protection against B.1.617.2 may not be quite as good as against the Kent variant, particularly for people who have only had one dose.

4. Will the 21 June ending of restrictions still go ahead?

It’s difficult to say at this point whether the final step of the coronavirus roadmap - the easing of all lockdown restructions - should go ahead on 21 June. The Government will make the decision by 14 June, and by then there will be more certainty about how and whether B.1.617.2 differs from other coronavirus variants.

If, at that point, there is firmer evidence that B.1.617.2 is easier to catch or that vaccines don't protect us as well against, it may be wise to hold off on ending restrictions entirely until a higher proportion of the population has been vaccinated. This is because a higher proportion of the population would need to be vaccinated in order to prevent another big wave of hospitalisations and deaths.

Worried about variants in your area?

If you live in an area where a new variant is spreading, you're advised to take extra precautions to stop the spread. This includes things such as getting tested regularly and meeting outdoors rather than indoors where possible.

Read more about these extra precautions and find out if you live in an affected area


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Last updated: Jul 28 2022

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