Orthrus CH.1.1: new Covid variant spreading in UK alongside Kraken as UKHSA issues warning

A Covid variant known as ‘Orthrus’ is spreading in the UK alongside the highly transmissible ‘Kraken’ strain.

The UK Health Security Agency (UKHSA) has warned that the new variant - officially known as CH.1.1 - is a sublineage of the Omicron BQ.1 and is currently at “moderate prevalence” in the country.

The health agency says this strain - and the Kraken sublineage known as XBB.1.5 - are most likely to take over from BQ.1 as the next dominant Covid variants in the UK, unless further novel variants arise. Neither of the strains have yet been designated as ‘variants of concern’ by the UKHSA, but are both being monitored.

A report by the health agency states that CH.1.1 has a 21.56% relative growth rate advantage over BQ.1.1 and has reached a prevalence of 15.78%.

Separate data from the Sanger Institute, a genomics and genetics research institute which assesses Covid strains circulating in the UK, shows that Orthrus accounted for 23.3% of all Covid tests analysed in England on 7 January, the latest figures available.

The strain, which was first detected in November, with a case reported in Blaby in the south west of Leicestershire. It has since been detected in the North East, West Yorkshire, East Midlands and southern England, with cases reported in areas including Northumberland, Bradford, Wakefield, Oxford and Reading, among others.

However, it should be noted that the Sanger data is only based on genomes sequenced for general surveillance and excludes those sequenced in special studies or with a known recent travel history. As the majority of positive Covid samples are not sequenced by the lab, it does not reflect the true number of cases,

Dr Meera Chand, director of clinical and emerging infections at the UKHSA, warned that getting vaccinated against Covid remains the “best defence” against serious illness amid the emergence of the new variants.

She said: "Through our genomic surveillance we continue to see evolution of variants in the Omicron family. UKHSA is constantly monitoring the situation and working to understand the implications for public health.

"Vaccination remains our best defence against future Covid-19 waves, so it is still as important as ever that people come forward and take up all the doses for which they are eligible as soon as possible."

The UKHSA issued advice earlier this month urging people to stay at home if they feel unwell and wear a face mask if they have to leave the house, in a bid to counter high levels of Covid, flu and invasive Strep A disease (iGas).

Professor Susan Hopkins, chief medical adviser at the UKHSA, also recommended that children stay home from school if they are unwell and have a fever. She said: “It’s important to minimise the spread of infection in schools and other education and childcare settings as much as possible. If your child is unwell and has a fever, they should stay home from school or nursery until they feel better and the fever has resolved.”

She added: “Adults should also try to stay home when unwell and if you do have to go out, wear a face covering. When unwell, don’t visit healthcare settings unless urgent, or visit vulnerable people.”

Kraken variant ‘most transmissible yet’

While Orthrus is behind more infections, experts have warned that the Kraken variant is “one to watch this year” amid concerns over how transmissible it is.

Concern about Kraken is largely due to how rapidly it is spreading in the United States, causing cases of the variant to more than double in a week. The strain now accounts for more than 40% of Covid cases in America, according to recent data releases from the Centers for Disease Control and Prevention (CDC), and it has been detected in at least 29 countries - including the UK.

It has been dubbed the “most transmissible yet” by the World Health Organisation (WHO) and is thought to be capable of evading vaccines. However, it is not thought to cause more serious illness than the original Omicron variant.

In a statement on Omicron sublineages BQ.1 and XBB.1.5, the WHO said: “The Omicron variant of concern remains the dominant variant circulating globally, accounting for nearly all sequences reported to GISAID[1].

“While we are looking at a vast genetic diversity of Omicron sublineages, they currently display similar clinical outcomes, but with differences in immune escape potential.

“The potential impact of these variants is strongly influenced by the regional immune landscape. While reinfections have become an increasingly higher proportion of all infections, this is primarily seen in the background of non-Omicron primary infections.

“With waning immune response from initial waves of Omicron infection, and further evolution of Omicron variants, it is likely that reinfections may rise further.”