This is how the new Covid strain mutated - and what causes a virus to change

A new strain of Covid-19 is spreading across the UK, and it’s thought to be up to 70 percent more transmissible than other variants.

Health Secretary Matt Hancock announced on Monday 14 December that the new strain had been identified in the south-east of England, and it has since been linked to the exponential rise in cases there.

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The rapid spread of the variant - called B117 - has led to the introduction of tighter coronavirus restrictions across the four nations, and many countries across the world enforcing travel bans on the UK.

Here’s everything you need to know about virus mutations, as scientists grapple to understand the new strain. 

Why do viruses mutate?

All viruses naturally mutate as they spread through a population, and this coronavirus Sars-CoV-2 has undergone one or two changes a month since the start of the pandemic. 

In fact, it has changed at a slow pace compared to other viruses, like seasonal flu, which mutates at a fast rate so that a new vaccine has to be introduced every year.

It is an RNA virus, like the flu and measles, and these types of viruses are more prone to mutations than DNA viruses, such as herpes and smallpox.

Mutations usually happen by chance, and don’t have much impact on the properties of a virus - the World Health Organisation (WHO) said these changes are “natural and expected”.

Often, they can lead to a weaker version of the virus, or the changes could be so small that there’s no difference in its behaviour. 

However, sometimes viruses can mutate in a way that helps the infection to spread. 

More worrying mutations are when the proteins on the surface of the virus are changed so it can evade the immune system - or if so many changes have been made that it is now very different to the original variant.

What is a mutation?

A mutation is a change in a virus’s genome, which is the set of genetic instructions that houses all the information the virus needs to function.

Mutations happen when the virus makes contact with a host and starts to replicate. 

The set of instructions is then copied, but mistakes can often happen in the process. 

Where the errors occur within the genome will determine whether they have a positive or negative impact on the virus’s ability to survive or replicate.

How did Covid-19 mutate?

As it has passed from person to person over the past few months, Covid-19 has been mutating.

Scientists think this new strain possibly mutated in a patient who had a weakened immune system and was unable to fight off coronavirus.

This could mean that the virus stayed in the patient’s body for a long period of time, which is why it was able to evolve.  

How are mutations detected?

Mutations can be detected through genome sequencing - a technique allowing scientists to monitor small changes in the virus to help to understand how it works. 

Across the world, scientists are working to sequence Sars-CoV-2 genomes.

By taking a swab from someone with coronavirus, the genetic code can be extracted before being "read" using a sequencer.

Genomes and mutations can then be compared, and scientists can share the information. 

Has Covid-19 mutated before?

SARS-CoV-2 has been constantly mutating over the past few months, but at a very slow pace.

The virus that was first detected in Wuhan is not exactly the same one that has spread across the world.

Generally, the new versions of the virus haven’t been much different to the original variant. 

A mutation - called D614G - was found in Europe in February and that became the globally dominant form of the coronavirus.

Another mutation, A222V, then spread across Europe and was linked back to people holidaying in Spain over the summer.

The new strain, B117, has caused concern because it is quickly becoming the dominant variant in south-east England.

It has certain mutations that affect the spike protein, which is the key the virus uses to attack our body's cells.

The variant is also causing concern because it seems to be much more transmissible - although there is no evidence that suggests it could cause a more serious illness. 

This particular mutation has also been spotted in Australia, Denmark, Italy, Iceland and the Netherlands.