Another variant of the virus has been found in Bristol, which scientists have labelled a new “variant of concern”. It’s the fourth variant of concern identified by the New and Emerging Respiratory Virus Threats Advisory Group (Nervtag).

Only three of these variants are circulating in the UK: the Kent variant, the South Africa variant and now the Bristol variant. The fourth is a variant that hails from Brazil, but hasn’t yet made it onto UK soil.

So, what makes a variant ‘cause for concern’? Well, viruses mutate quite often and most of the time, they mutate in a way that doesn’t change much about their characteristics. There are around one to two mutations of SARS-CoV-2 per month, which means many thousands of mutations have developed since the virus emerged in 2019, according to the Covid-19 Genomics UK Consortium.

“Most of these mutations have no effect on the behaviour of the virus but occasionally a mutation occurs that alters how quickly the virus spreads, how infectious it might be or even the severity of the disease it causes,” says Professor Lawrence Young, a virologist and expert in molecular oncology from Warwick Medical School. “It is then the virus becomes a variant of concern.”

In the UK, a proportion of positive test results are sequenced so public health agencies can understand how the virus is behaving in certain areas. This means they can implement new measures if cases appear to be rising more rapidly than expected, or there are more hospitalisations or deaths than normal.

Here’s what we know about the three variants of concern in the UK so far.

The Kent variant

This variant, known as VOC202012/01, was first detected in the UK back in September 2020. It includes multiple mutations in the spike protein, which is the part of the virus that first attaches to a human cell and then infects us.

These changes have resulted in the virus becoming about 50% more infectious, according to Public Health England (PHE), meaning it’s spreading far more easily between people.

There’s also a possibility that being infected with the variant is associated with an increased risk of death compared to earlier versions that were circulating.

Early evidence suggests the new variant could be about 30% more deadly, says PHE, but more data are being collected and the position will become clearer over the coming weeks.

The absolute risk of death is still low, the health body adds.

The South Africa variant

This variant, called VOC202012/02 or 501 Y.V2, appears to have emerged around the same time as the variant originating in the UK – but in South Africa. It shares the same mutation to the spike protein as the UK variant, but also has a number of other mutations including E484K.

It’s thought the E484K mutation may be able to escape the body’s antibodies to some extent and is therefore of potential public health concern. The main worry being that it could impact vaccine effectiveness.

People in certain parts of the UK where this variant is spreading are being asked to stay home and undergo “surge testing” to minimise its spread.

The Bristol variant

This variant, called VOC 202102/02, is the most recently discovered variant in the UK, with 21 cases found in England to date – 15 in Bristol and the south west of England, and six cases elsewhere. 

The Bristol mutation – colloquially named so because it was first discovered in the city – is a variant of the strain identified in Kent, meaning it’s likely to be more transmissible. Like the South Africa variant, it also carries the spike mutation E484K, which experts suggest may be better at evading the human immune response – and therefore could have an impact on vaccines. 

PHE notes it’s “very unusual for any variant virus to render a vaccine completely ineffective”, however variants can alter the performance of vaccines. 

Prof Young says it’s “likely” we’ll see more variants of concern, “as the virus adapts to our bodies and learns ways to dodge our immune response”.

“The more the virus spreads, the more chances it has to evolve and to pick up other mutations,” he explains.

“So getting vaccines rolled out quickly along with other ways to prevent transmission – social distancing, etc – will help stop infection and the generation of new variants. Whatever virus variants may arise, they are all transmitted in the same way: person to person contact.”