Covid: New strain, variant or mutation? What’s the difference?

Boris Johnson’s government announced last week that a new “variant” of Covid-19 had been detected which could be responsible for the faster transmission of the virus recently seen in London and the south-east of England.

The prime minister then cancelled five-day Christmas bubble plans and moved almost 18 million people into a newly created tier 4, after his advisers warned of the new variant’s rapid spread.

Reports from the media and government alike have also referred to a new “strain” of the virus, often dubbing it a “mutant” version of the coronavirus. So what is this new development – and what exactly is the difference between variant, strain and mutation?

What is the Covid-19 variant?

The new Covid-19 variant – called VUI 202012/01 – spreads far more easily between people as a result of a series of mutations that have been identified in the genetic coding.  

It is not, however, believed to cause more severe symptoms of the Covid-19 disease, or lead to higher rates of mortality. And all current evidence suggests the vaccines remain effective against the variant.

Imperial College London experts have said the variant could make Covid-19 around 70 per cent more transmissible, and the government fears it could increase the country’s R rate of transmission by 0.4 or more if allowed to spread unchecked.

So it’s a variant – not a strain?

Yes. The term strain is only appropriate when referring to Sars-Cov-2, the virus causing the Covid-19 disease – since it is a strain of the wider coronavirus family, including severe acute respiratory syndrome (SARS) and the Middle East respiratory syndrome (MERS).

At a briefing organised by the UK’s Science Media Centre on Tuesday, Prof Tom Connor of the School of Biosciences at Cardiff University explained: “There is one strain of coronavirus. That is Sars-Cov-2. That is the single strain, and there are variants of that strain. These are variants.”  

Prof Connor said the term strain is often misused. “The correct term to use is variant to describe this particular variant of concern.”

What about mutation?

Mutation is the process by which a strain can take on new variants. The idea of a mutating or “mutant” virus may sound frightening – but scientists have made clear it is normal and expected.

Some of these mutations are “silent” and don’t have any function, but others have made some significant changes to the biology of Sars-CoV-2. One of these mutations, known as N501Y, sits in the so-called ‘spike’ protein – the part of the virus which is responsible for binding to human cells.

The mutation has increased the ability of the spike receptor to attach to certain proteins that cover our own cells, therefore making it more infectious.

A second notable mutation, named 69-70del, leads to the loss of two amino acids in the spike protein and the evasion of the immune response in some immunocompromised patients, evidence shows.

Although it’s unlikely that any single change to the virus would make a working vaccine less effective, the vaccine may need to be altered as a greater number of mutations develop.