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A new strain, known as NB.1.8.1, has been and is under close scrutiny by global health authorities amid signs of wider international spread. The , first identified in January 2025, has now been confirmed in Northern Ireland, Wales and some popular British tourist destinations, although the full extent of its transmission remains unclear due to a decline in testing and genomic surveillance.

The World Health Organisation (WHO) has classified NB.1.8.1 as a "variant under monitoring", meaning it is being watched for any signs of increased transmissibility or severity. Globally, NB.1.8.1 now accounts for more than 10% of recorded infections and has been found in countries including the United States, Australia, Thailand, China and Hong Kong. While early data suggests it may infect human cells more efficiently than previous Omicron offshoots, there is no current evidence that it leads to more severe illness.

Health experts say the symptoms linked to NB.1.8.1 are largely in line with other recent Covid strains.

They include fatigue, fever, muscle aches and sore throat, though some patients have also reported gastrointestinal symptoms, which are less common in other variants.

As with earlier mutations, symptoms can vary in intensity, particularly among those with underlying health conditions or compromised immune systems.

The UK Health Security Agency (UKHSA) has not issued a specific update on NB.1.8.1, but officials continue to monitor the variant through international data-sharing efforts and existing surveillance programmes.

In a recent update, the WHO said: "NB.1.8.1 carries mutations that may enhance infectivity, but current evidence does not suggest increased disease severity. Continued monitoring and research are required."

Although Covid-19 case numbers in the UK have remained relatively low through early 2025, experts warn that waning immunity and reduced testing may allow new variants to spread unnoticed.

Vaccines remain effective at preventing serious illness and hospitalisation, though their efficacy against infection tends to decline over time, particularly with new mutations.

Health officials continue to urge eligible individuals to stay up to date with booster doses.

Members of the public are advised to remain cautious, particularly when travelling internationally or visiting crowded indoor spaces, and to stay informed through official health channels.