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The UK is seeing rising cases of coronavirus caused by a variant called Delta, which was first identified in India.
Experts say it is more transmissible than even the “UK/Kent” or Alpha variant which previously dominated here.
Delta is behind almost all new Covid infections.
There are thousands of different variants of Covid circulating across the world. One of them, called Delta or B.1.617.2, appears to be spreading more quickly in some countries, including the UK.
Viruses mutate all the time and most changes are inconsequential. Some even harm the virus. But others can make the disease more infectious or threatening – and these mutations tend to dominate.
Those with the most potentially concerning changes are called “variants of concern”. They are kept under the closest watch by health officials, and include:
- Delta (B.1.617.2) which currently accounts for 99% of new Covid cases in the UK
- Alpha (B.1.1.7), first identified in the UK but which has spread to more than 50 countries and appears to be mutating again
- Beta (B.1.351), first identified in South Africa but which has been detected in at least 20 other countries, including the UK
- Gamma (P.1), first identified in Brazil but which has spread to more than 10 other countries, including the UK
There is no evidence that any of them cause much more serious illness for the vast majority of people.
As with the original version, the risk remains highest for people who are elderly or have significant underlying health conditions.
But a virus being more infectious and equally dangerous will in itself lead to more deaths in an unvaccinated population.
Vaccines offer high protection against severe illness with Covid-19, including infections caused by variants of concern. The shots also reduce the risk of infection. But they are not perfect and do not completely eliminate all risk.
The advice to avoid infection remains the same for all strains: wash your hands, keep your distance, wear a face covering and be vigilant about ventilation.
The variants of concern have all undergone changes to their spike protein – the part of the virus which attaches to human cells.
Delta has some potentially important ones (such as L452R) that might make it spread more easily.
There is no evidence to indicate it causes more severe disease or might make current vaccines less effective, say UK officials.
One mutation, called N501Y, shared by the Alpha, Gamma and Beta, seems to make the virus better at infecting cells and spreading.
Beta and Gamma also have a key mutation, called E484K, that may help the virus sidestep some of the body’s immune defences.
Experts recently found a small number of cases of Alpha with this change too.
Current vaccines were designed for earlier versions of coronavirus, which means they may not be the ideal match for new variants and so might not work quite as well.
But experts say they are still very effective at protecting lives by cutting the risk of severe illness:
- An analysis by Public Health England found two doses of either the Pfizer or AstraZeneca vaccine was more than 90% effective against hospitalisations for Covid-19 caused by Delta
- A single dose, however, was less effective at preventing illness from Delta, compared to how well it worked against Alpha.
Doctors say it is vital that people get both doses to gain maximum protection against existing and emerging variants.
Experts are confident existing vaccines can be redesigned to better tackle emerging mutations.
The UK government has a deal with biopharmaceutical company CureVac to develop vaccines against future variants, and has pre-ordered 50 million doses.
Depending on how variants continue to develop, these could potentially be used to offer a booster vaccine to older or clinically vulnerable people later in the year.