Covid variant Orthrus now accounts for one-fifth of Covid cases in England, figures show.

Surveillance data shows how the strain, scientifically called CH.1.1, has snowballed since it was first detected in November 2022. 

Health chiefs have warned that it — or another Omicron sub-lineage nicknamed the 'Kraken' — could soon become dominant. 

With both Kraken and Orthrus surging in the UK - we have put together a guide about Covid-19 currently in the UK.

Here is what we know so far:

What is Orthrus?

Since the first cases of the new variant emerged in November it spread to account for 23.1 per cent of all cases in England by 1 January, the latest UKHSA figures show – though sequencing suggests it could make up as much as 100 per cent in some areas.

The figures for that week suggest Orthrus accounted for around 8,700 cases, though officials warn variant estimates are uncertain.

Orthrus, along with the Kraken, or XBB.1.5, variant are thought to be moving towards dominance in Britain – though neither have been classed as being “of concern”.

How worrying are the Orthrus and Kraken variants?

Data from the Sanger Institute, one of the UK's largest surveillance sites tasked with analysing strains circulating in the UK, shows Orthrus, nicknamed after a mythical two-headed dog, accounted for 23.3 per cent of all Covid tests analysed in England on January 7, the latest data available.

But the Sanger data is only based on hundreds of samples, meaning it does not reflect the true picture. 

Why are they called the Kraken and Orthrus variants?

Kraken, nicknamed after a mythical sea monster, currently accounts for 3.6 per cent of cases in England, according to the same data. 

However, it was only spotted in mid-December.

While Orthrus is behind more infections, experts have said Kraken appears to be growing faster and is thought to be more transmissible and immune evasive than other strains in circulation. 

UK Health Security Agency data suggested that Kraken has a 39 per cent growth rate advantage over BQ.1, the current dominant variant.

Meanwhile, the advantage rate for Orthrus was 22 per cent.

However, the UKHSA cautioned Kraken's current low prevalence in the UK makes any estimate of its growth 'highly uncertain'.   

Neither Covid variant has been escalated to being declared a 'variant of concern' by the UKHSA.

How worrying is this for the NHS?

There are no signs they cause more severe disease than other, similarly mild Omicron strains, nor are sufficiently genetically divergent as to cause Covid vaccines to be less effective.  

However, scientists have found both host concerning genetic quirks.

Orthrus has a mutation called P681R — which was also on the Delta variant — and is thought to make it better attack cells and cause more severe illness. 

Scientists have also spotted it has R346T, which is thought to help the strain fight-off antibodies that were generated in response to vaccination or previous infection.

And Kraken has one called F486P, which helps it to bypass Covid-fighting antibodies. Another mutation — S486P — is thought to improve its ability to bind to human cells.

Concerns over the two new strains, combined with the unfolding NHS crisis and a 'flu-nami', has triggered calls for the return of pandemic-era restrictions like masks and working-from-home in a bid to ease pressure on the ailing health service. 

What is the picture of Covid-19 in the UK?

The latest data from the Office of National Statistics (ONS) suggests Covid cases have actually fallen in England.

According to the data, 2.2 million people, or one in 25 people, were infected with the virus in the week to January 3.

ONS analysts estimated that the total was 11 per cent lower than the week before. 

However, as many as one in 14 people were still infected in the worst-affected parts of the UK.

And some have suggested it could be the calm before another wave of infections.  

What is the picture in the North East?

Data for England showed cases fell in all regions apart from the North East, where 4.1 per cent of people were infected — up from 3.8 per cent one week earlier.

Infections were highest in the East Midlands, South West and South East, where 4.5 per cent were thought to be carrying the virus.

Cases were lowest in London and the North West, where 3.5 per cent were infected, according to ONS estimates. 

But the ONS, which swabs thousands of people across the UK to estimate how prevalent the virus is, noted that these estimates are based on a lower than usual number of swabs due to the festive period.  

Warnings about the new variants also came as the number of people infected with Covid taking up hospital beds in England is falling. 

The figure dropped 11 per cent from 9,414 in the week to January 4 to 8,404 in the seven days to January 11. 

NHS data shows Covid patients peaked at 9,533 on December 29 and has since fallen 19 per cent to 7,743.