What is new ‘Nimbus’ Covid variant? Symptoms as cases grow in UK

Cases have been confirmed England and in ‘small pockets’ across the UK

Covid-19 is once again making headlines more than five years after the initial outbreak, with a new variant spreading in the UK and several countries across the globe.

The new strain, named NB.1.8.1 and also known as ‘Nimbus’, now accounts for just over 10 per cent of global infections, with cases now confirmed in England and Northern Ireland.

While there is no evidence that the new strain causes more severe symptoms, experts believe that it in can infect cells more efficiently and can trigger gastrointestinal symptoms such as diarrhoea, constipation and nausea.

Since first being recognised in January 2025, the omicron variant has spread to several states across the US, Australia, Thailand and is the most dominant variant in China and Hong Kong.

Due to fewer people testing for Covid, it is increasingly difficult for experts to track infections (Getty/iStock)

What is ‘Nimbus’ NB.1.8.1?

The World Health Organisation has designated the NB.1.8.1 as a “variant under monitoring”, and comprises around 10.7 per cent of all submitted sequences.

A WHO spokesperson said: "SARS-CoV-2 continues to evolve, and between January and May 2025, there were shifts in global SARS-CoV-2 variant dynamics. At the beginning of the year, the most prevalent variant tracked by WHO at the global level was XEC, followed by KP.3.1.1.

"In February, circulation of XEC began to decline while that of LP.8.1 increased, with the latter becoming the most detected variant in mid-March. Since mid-April, the circulation of LP.8.1 has been slightly declining as NB.1.8.1 is increasingly being detected."

While it first appeared in samples at the beginning of this year, data from GISAID, a global data of genetic sequences of major disease-causing viruses, show that the first known cases were registered at the end of April.

NB.1.8.1 has been detected in the US, China, Thailand and Australia (Getty/iStock)

What are the symptoms?

While evidence has suggested that NB.1.8.1 may spread more easily than other variants, the WHO has not observed any signs that it has an increase in severity.

"Data indicates that NB.1.8.1 does not lead to more severe illness compared to previous variants, although it appears to have a growth advantage, suggesting it may spread more easily," Subhash Verma, a professor of microbiology and immunology at the University of Nevada, Reno School of Medicine, told CBS News.

"In other words, it is more transmissible."

Common symptoms align with typical Omicron subvariants and include fatigue, fever and muscle aches.

Dr Naveed Asif, GP at the London General Practice, warned the variant also has a distinctive symptom, a severe sore throat known as “razor blade” throat, causing a sharp stabbing pain when you swallow, often at the back of the throat.

So far, cases have been recorded in England, Northern Ireland and Wales, as well as in popular British tourist hotspots overseas. However, given the dwindling numbers of people testing for Covid-19, it has become increasingly difficult to know the true number of infections.

Why has there been a global surge in cases?

The “Nimbus” variant, as it has been dubbed, does appear to be more transmissible than previous strains, with notable increases reported in India, Hong Kong, Singapore and Thailand.

Dr Chun Tang, GP at UK private healthcare centre Pall Mall Medical, said: “NB.1.8.1 isn’t too different from the Omicron variant, but it does have some tweaks to its spike protein, which might make it spread a bit more easily or slip past some of our existing immunity.

“That said, early signs suggest it doesn’t seem to cause more serious illness, but of course, we’re still learning more about it.”

Do the Covid vaccines work against NB.1.8.1?

Current Covid jabs are expected to remain effective against this variant and protect anyone infected from severe illness.