Health experts are warning of a rising number of cases in the UK linked to a newly identified Covid strain, known as NB.1.8.1 or “Nimbus.” According to the UK Health Security Agency (UKHSA), this variant is becoming increasingly common worldwide and has now been detected in at least 13 UK cases.

Countries including China, Hong Kong, and Ireland are also seeing sharp increases. NB.1.8.1 presents many of the familiar Covid symptoms - fever, congestion, and fatigue - but doctors note a particularly intense sore throat, described as a “razor blade sensation,” alongside swollen glands and redness in the throat. Gastrointestinal issues such as nausea, bloating, diarrhoea, and heartburn have also been reported more frequently in this strain.

Despite its higher transmissibility, health officials currently have no evidence to suggest that NB.1.8.1 causes more severe illness or that existing vaccines are less effective. The World Health Organization has placed the variant under observation due to its rapid global spread since it first emerged in early 2025.

Medical professionals continue to urge the public to remain alert. While the variant is not yet dominant in the UK, rising case numbers abroad suggest it could become more widespread in the coming weeks.