How does a virus mutate? Why do mutations happen as South African, UK and Brazil Covid variants continue to spread

This is what causes a virus to mutate – and how long it takes

Three new variants of coronavirus are causing widespread concern – the South African, UK and Brazil strains.

The UK strain, first detected in Kent, has been linked to the exponential rise in cases in the country and is now the dominant variant here.

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It recently changed again to adopt the mutation, called E484K, that is already seen in the South Africa variant.

All viruses naturally mutate as they spread through a population (Shutterstock)

The rapid spread of the UK strain - called B117 - led to the introduction of fresh national lockdowns in Scotland and in England, and many countries across the world enforcing travel bans.

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

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 UK strain, B117, has caused concern because it has certain mutations that affect the spike protein, which is the key the virus uses to attack our body's cells.

Some research appears to show that mutation E484K, also found in the South African and Brazil strains, may help the virus to evade the immune system’s antibodies.

However, there is currently no evidence to suggest that the approved vaccines will not work against these variants – although experts think effectiveness of the jab could be reduced.