Both strains have been spreading rapidly
As temperatures plummet and we venture further into autumn and winter, respiratory illness rates start to surge – from ordinary colds to flu and coronavirus. Currently, two new Covid strains are doing the rounds in the UK, spreading rapidly to become the dominant versions of the disease.
The World Health Organisation (WHO) recognises the XFG variant as the newest COVID-19 strain and currently the most widespread throughout the UK. First detected in January 2025, it’s more commonly referred to as Stratus, whilst another strain presently “under monitoring” is NB.1.81, also known as Nimbus. Like Stratus, it’s thought to be extremely contagious, though it doesn’t seem to trigger more severe symptoms than other Omicron variants.
The WHO states: “Our genomic surveillance of SARS-CoV-2 lineages last month found that 35 per cent were classified as XFG.3, 28 per cent were classified as XFG, 11 per cent were classified as NB.1.8.1, seven per cent were classified as XFG.5 and seven per cent were classified as XFG.3.4.1.” The WHO’s latest data can be accessed in its National flu and COVID-19 surveillance reports, reports the Express.
Current WHO evidence doesn’t indicate these variants trigger more severe illness than other circulating variants. The WHO continues: “It’s normal for viruses to mutate and change. As more data becomes available on these variants, we’ll have a better understanding of how they interact with our immune systems and how to optimise our protection, as well as actions we can take to keep the most vulnerable safe and live our lives as normally as possible. The most important thing is for those eligible to get their vaccination when it is due.”
As of late September 2025, the WHO states that the dominant COVID-19 strain across the UK is the Stratus variant, which includes the Omicron subvariant XFG and its offshoots, particularly XFG. 3. The Nimbus variant (NB. 1.8.1) remains present, though it’s no longer the predominant strain.
Stratus symptoms
It’s vital to remember that the virus continues to evolve, and this information may change as new variants emerge while others fade away. Regarding the key characteristics of Stratus and its most common symptoms, many experts emphasise that the primary sign to look out for is a hoarse or gravelly voice, which can serve as an early warning of infection.
Stratus is thought to spread quite easily, leading to a rise in cases across various regions. Besides a hoarse voice, you might also experience:
- sore throat
- nasal congestion
- blocked nose
- digestive problems
- feeling really tired
Existing vaccines are expected to offer strong protection against severe illness and hospital admission. The WHO has rated the additional public health risk posed by Stratus as “low” on a global scale.
Nimbus symptoms
Research indicates that NB. 1.8.1 exhibits a strong affinity for the ACE2 receptor, allowing it to penetrate cells more effectively than previous variants. Numerous doctors have noted that a distinguishing feature of this strain is an extremely painful sore throat, often characterised as a “razor blade sensation” during swallowing.
This variant has also been linked to heightened occurrences of gastrointestinal symptoms, including nausea, diarrhoea, bloating, and abdominal discomfort. Nimbus develops through genetic recombination, making it a fusion of various Omicron subvariants.
Current evidence suggests that NB. 1.8.1 does not trigger more severe illness compared to other circulating variants. Existing vaccines remain highly effective in providing protection against serious disease. In May 2025, the WHO designated Nimbus as a “Variant Under Monitoring” (VUM), a category for variants that could potentially threaten public health.
Nimbus was first identified in January 2025 and rapidly expanded throughout Asia before emerging in multiple countries worldwide, including the UK, US, and Australia. It became one of the predominant strains in several regions.
Every major COVID-19 strain so far
- Alpha (B.1.1.7): First detected in the UK in late 2020
- Beta (B.1.351): First reported in South Africa in late 2020
- Gamma (P.1): First detected in travellers from Brazil in early 2021
- Delta (B.1.617.2): First reported in India in late 2020 and became the dominant strain worldwide until Omicron
- Omicron (B.1.1.529): First reported in South Africa in late 2021, this lineage and its subvariants have dominated globally ever since
Major Omicron subvariants
- BA.1, BA.2, BA.3, BA.4, BA.5:These early sub-lineages drove infection waves throughout 2022
- BA.2.86 (Pirola):Noted for its high number of mutations, prompting close monitoring in 2023
- EG.5 (Eris):A dominant strain in 2023
- JN.1:A fast-spreading Omicron subvariant prominent in late 2023 and early 2024
- KP.2 (FLiRT):A subvariant of JN.1, part of the “FLiRT” family of variants prominent in mid-2024
- XEC (Stratus): Became the dominant global strain in early 2025
What to do if you think you have Covid
If you’re showing signs of a respiratory infection like COVID-19, such as a fever or generally feeling unwell, it’s recommended to avoid contact with vulnerable individuals and stay at home if possible. For those who absolutely must leave their homes, the Living with COVID guidelines remain unchanged and can help minimise the risk of transmitting your infection to others:
- Make sure to wear a snug face covering with multiple layers or a surgical mask
- Stay away from crowded spots like public transport, big social events, or any enclosed areas that aren’t well-ventilated
- Try to do your exercise outside in places where you won’t be close to others
- Always cover your mouth and nose when you cough or sneeze
- Wash your hands often with soap and water for 20 seconds or use hand sanitiser after coughing, sneezing, or blowing your nose, and before eating or handling food and avoid touching your face
Can I get a Covid vaccine?
The WHO states: “Vaccines remain our best defence against severe disease and hospitalisation from flu and COVID-19.” Information on eligibility and booking vaccinations can be found here.
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