Scientists deliver verdict on new Covid variant NB.1.8.1 that could become 'dominant strain'

Evidence so far suggests NB.1.8.1 may spread more easily than earlier Covid strains

A new Covid-19 variant has been added to a World Health Organization (WHO) watch list, more than five years after the virus was declared a pandemic.

Called NB.1.8.1, the variant is circulating across the globe and is responsible for a spike in cases in Australia, Thailand and China among other countries.

By late April 2025, the new variant made up roughly 10.7 per cent of all detected Covid strains – up from just 2.5 per cent four weeks prior, according to the WHO.

While the overall health risk remains low, experts are closely monitoring the new variant, as some regions have seen rising infections and hospitalisations where it has been detected.

For example, the government in Thailand has issued a warning after 257,280 Covid cases and 52 deaths following outbreaks in the capital Bangkok and in the Chonburi Province.

Deputy government spokesperson Anukool Pruksanusak said international travel and the upcoming rainy season could worsen the outbreaks and the Ministry of Public Health will monitor the situation closely.

What is NB.1.8.1?

The NB.1.8.1 variant was first recorded on January 21 and was designated a "variant under monitoring" by the WHO on May 23.

The WHO has released a report which says the strain could potentially be more transmissible than other previous variants. However, it does not appear to cause worse symptoms.

The report said: "Despite a concurrent increase in cases and hospitalisations in some countries where NB.1.8.1 is widespread, current data does not indicate that this variant leads to more severe illness than other variants in circulation."

It added: "WHO recommends that countries remain vigilant, adapt to evolving epidemiological trends, and leverage COVID-19 management strategies to strengthen systems for all respiratory disease threats.

"Member States should continue offering COVID-19 vaccines in line with WHO recommendations. Based on the current risk assessment of this event, WHO advises against imposing travel or trade restrictions."

The WHO detailed in the report that certain mutations on the new strain of the virus "could increase the variant’s transmissibility".

The new strain was detected by scientists monitoring case numbers and Covid strains in circulation.

"NB.1.8.1 is one of the most recent SARS-CoV-2 variants in circulation," explains Francois Balloux, Professor of Computational Systems Biology and Director at the UCL Genetics Institute.

"It likely originated through a recombination event between a previous Omicron recombinant called XDE and Omicron JN.1, the direct descendent of BA.2.86 (aka Pirola)," Prof Balloux told the Manchester Evening News.

'Recombination' occurs when a new variant arises from the genetic mixing of two or more variants. In this case, the new variant is most likely from a mixing of the Covid XEC variant and JN.1 variant.

He added: "It has been spreading mostly in Australia and Asia. There have been relatively few cases reported in Europe so far with only four genomes sequenced from the UK."

Should you be concerned about NB.1.8.1?

So far, NB.1.8.1 does not seem to cause more severe illness than previous variants, but Prof Balloux says it could be "here to stay".

"It looks like a well-adapted variant with a strong binding affinity to the ACE2 cell receptors that the virus uses to infect us," he says, adding that previous Covid infection or vaccination may not protect against the new variant."

"It also bypasses to some extent antibodies mounted during vaccination and infection by previous strains," Prof Balloux explains.

He added: "It may be here to stay and might even replace the current dominant strains next winter. This being said, it is most unlikely to cause surges of severe [illness] such as those we witnessed during the pandemic."

According to the WHO, the global health risk from the NB. 1.8.1 variant is low. Covid vaccines are also expected to remain effective against this new variant and help to protect against severe disease, the organisation says.

What are the symptoms of the new Covid variant?

Symptoms of the new strain are believed to be the same as earlier versions of the Covid virus.

"It is fairly unlikely that NB.1.8.1 will cause different symptoms than the other Omicron strains that have been in circulation over the last three years," Prof Balloux confirms.

According to the NHS, common Covid symptoms include:

• A high temperature or shivering (chills)
• A new, continuous cough
• A loss or change to your sense of smell or taste
• Shortness of breath
• Feeling tired or exhausted
• An aching body or a headache
• A sore throat, blocked or runny nose
• Loss of appetite, feeling sick or being sick
• Diarrhoea