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As autumn unfolds in the UK, the rise of new Covid strains is causing infection numbers to climb again. Currently, two main variants, named Nimbus (NB. 1.8.1) and Stratus (XFG), are primarily driving the increase, as reported by the UK Health Security Agency (UKHSA). The World Health Organization has placed Nimbus (NB.1.8.1) under the “variant under monitoring” category as of September 4, 2025.
The Stratus variant is responsible for more than three-quarters of the cases, while the Nimbus variant accounts for approximately 10% of sequenced cases. The UKHSA mentioned: “Presently, the most prevalent variants are XFG and NB.1.8.1, which are often termed Stratus and Nimbus in the media.”
“In our latest genomic surveillance of SARS-CoV-2 lineages, we found that 35% were identified as XFG.3, 28% as XFG, 11% as NB.1.8.1, 7% as XFG.5, and another 7% as XFG.3.4.1.”
Despite the increase in cases, health experts emphasize there’s no need for panic as these variants do not seem to cause more severe symptoms compared to earlier Covid strains. Their spread is considered part of how viruses naturally evolve over time.
The symptoms associated with these new variants largely resemble those of previous Covid cases, with some additional details worth mentioning. Individuals with the Stratus variant often experience a hoarse or scratchy voice early on.
Other commonly reported symptoms include nasal congestion, runny nose, fatigue, headaches, and mild fever. Infections with the Nimbus (NB.1.8.1) variant typically feature a “razor-blade” sore throat, characterized by sharp pain, particularly noticeable 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.
