As new Covid variants sweep across the UK this autumn, cases are climbing once again, with two strains now leading the surge. The Nimbus and Stratus variants also known as NB. 1.8.1 and XFG are the most common at the moment, according to the UK Health Security Agency (UKHSA). The World Health Organization currently classifies Nimbus (NB.1.8.1) as a “variant under monitoring” as of September 4, 2025.
The Stratus variant currently accounts for over three quarters of infections, while the Nimbus variant represents about 10% sequenced cases. The UKHSA wrote: “The most common current variants are the XFG and NB.1.8.1 (sometimes referred to in the media as the Stratus and Nimbus variants).
“Our genomic surveillance of SARS-CoV-2 lineages last month found that 35% were classified as XFG.3, 28% were classified as XFG, 11% were classified as NB.1.8.1, 7% were classified as XFG.5 and 7% were classified as XFG.3.4.1.”
Health experts, however, say there’s no cause for alarm, as these variants don’t appear to cause more severe illness than earlier strains of Covid and their emergence is part of the normal pattern of how viruses change over time.
The symptoms people are reporting with these new variants closely mirror previous Covid signs, but with a few differences worth noting. Many with the Stratus variant describe a hoarse, raspy or scratchy voice as one of the earliest warning signs.
Nasal congestion, runny nose, fatigue, headaches, and mild fever are also frequently reported. Nimbus (NB.1.8.1) infections often come with a “razor‑blade” sore throat, an intense, sharp pain in the throat, especially when swallowing or speaking.
Alongside that, patients may experience persistent fatigue, mild cough, muscle aches, fever, and sometimes digestive symptoms like nausea or diarrhoea, which are less often associated with earlier variants, according to the latest reports.