As temperatures drop and we move deeper into autumn and winter, respiratory illness rates begin to climb – everything from common colds to influenza and coronavirus. At present, two particular COVID strains are grabbing attention due to their rising dominance.
The World Health Organisation (WHO) identifies the XFG variant as the latest COVID-19 strain and presently the most widespread across the UK. Initially identified in January 2025, it’s more frequently called Stratus.
Whilst Stratus represents the newest addition, another strain currently “under monitoring” is NB.1.81, alternatively known as Nimbus, reports the Mirror.
Similar to Stratus, it’s believed to be highly transmissible, although it doesn’t appear to cause more serious symptoms than other Omicron variants.
The WHO says: “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.” The WHO’s most recent information can be found in its National flu and COVID-19 surveillance reports.
Present WHO evidence doesn’t suggest these variants cause more serious disease than other circulating variants. The WHO adds: “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 the dominant COVID-19 strain across the UK is the Stratus variant, which encompasses 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.
What is Stratus and its symptoms?
It’s crucial to note that the virus continues evolving, and this information may shift as fresh variants appear whilst others disappear. Concerning the key features of Stratus and its most frequent symptoms, numerous experts highlight that the primary indicator to watch for is a hoarse or gravelly voice, which can manifest as an early warning of infection.
Stratus is believed to transmit rather readily, which has resulted in a surge of cases across different regions. Beyond a hoarse voice, you may also encounter:
- sore throat
- nasal congestion
- blocked nose
- digestive problems
- feeling really tired
Current evidence doesn’t suggest that Stratus triggers more serious illness or proves more lethal than other variants presently in circulation.
Certain health experts suspect that Stratus might be more capable of bypassing immunity from previous infections or jabs. Existing jabs are anticipated to provide robust defence against serious illness and hospital admission.
The WHO has assessed the additional public health threat that Stratus presents as “low” on a worldwide basis.
What is Nimbus and its symptoms?
Studies suggest that NB.1.8.1 demonstrates a powerful attraction to the ACE2 receptor, enabling it to infiltrate cells more efficiently than earlier variants.
Multiple medics have observed that a characteristic symptom of this strain is an intensely painful sore throat, frequently described as a “razor blade sensation” when swallowing.
This variant has also been associated with increased instances of digestive symptoms, encompassing nausea, diarrhoea, bloating, and stomach pain.
Nimbus emerges through genetic recombination, creating it as a blend of different Omicron subvariants. Present evidence indicates that NB.1.8.1 does not cause more serious illness when compared to other circulating variants.
Current vaccines continue to deliver effective protection against severe disease. In May 2025, the WHO classified Nimbus as a “Variant Under Monitoring” (VUM), a classification for variants that might pose risks to public health.
Nimbus was initially detected in January 2025 and swiftly spread across Asia before appearing in numerous nations globally, including the UK, US, and Australia. It emerged as one of the dominant strains in certain regions.
What should people who think they have COVID do?
If you’re exhibiting symptoms of a respiratory infection like COVID-19, such as a fever or general malaise, it’s advisable to avoid contact with vulnerable people 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.
The NHS says: “The symptoms are very similar to symptoms of other illnesses, such as colds and flu. Most people feel better within a few weeks, but it can take longer to recover. For some people, it can be a more serious illness and their symptoms can last longer.” If you have a cough, you can ask a pharmacist for advice about cough treatments.
Are there still COVID vaccines?
The WHO states: “Vaccines remain our best defence against severe disease and hospitalisation from flu and COVID-19.” Information on eligibility and how they can book their vaccination here.
