The XFG variant — also known as American Covid or Stratus — is surging across the UK, with hospitalisations jumping from 950 in August to nearly 5,000 in September. The warning issued earlier this week that American Covid is spreading is now being borne out, with thousands of people suddenly experiencing its severe symptoms.
The new strain — also known as XFG or Stratus Covid — has joined other viruses in circulation this autumn, prompting an alert from the UK Health and Security Agency (UKHSA), whose latest figures revealed that positive cases recorded in hospital settings had climbed from 5.9 per cent to 7 per cent in just a matter of weeks.
Hospitalisations and case numbers
The UKHSA logged 1,374 cases in August, but by September those numbers had rocketed by 230 per cent to a staggering 4,589, with hospitalisations rising at an even more alarming rate, jumping from 950 in August to 4,939 the following month. As with many recent variants, American Covid presents with its own distinct set of symptoms.
According to Stony Brook Medicine, the majority of people are likely to experience mild cases of American Covid, particularly if they have received a vaccination or booster jab. The university has nevertheless urged people to remain vigilant for potential symptoms, as many vulnerable individuals could still be seriously affected by the illness.
Key symptoms and warning signs
Key symptoms of the variant include a persistent, dry cough, fatigue or general tiredness and a high temperature of 38C+. The variant may present with more than half a dozen additional signs, experts have cautioned, ranging from a scratchy, sore throat to episodes of diarrhoea.
Other potential symptoms include shortness of breath, feeling sick (nausea), loss of appetite or stomach aches, headaches and muscle pain, brain fog or trouble concentrating, sinus congestion or a runny nose.
There are certain warning signs that require urgent medical attention, with the NHS advising that people experiencing the following should ring 999 immediately:
- Feeling very suddenly and severely unwell, with symptoms only continuing to get worse
- Sudden chest pain
- Intense breathlessness that prevents people from finishing even short sentences, even while resting
- Breathing suddenly gets worse
- Coughing up blood
- Collapsing, fainting, or other loss of consciousness, and experiencing a seizure for the first time
- Inability to wake or stay awake
- New confusion
- Lips, nail beds and skin appearing pale, gray or blue - depending on skin tone
- A rash that behaves in the same way as meningitis - it does not fade when a glass is rolled over it
Precautions and expert advice
Britons who suspect they may have caught the virus have been urged to take precautions to prevent spreading it further throughout their communities. They have been told to avoid contact with others for at least five days, while anyone under the age of 18 should wait a minimum of three days.
Anyone receiving a positive test result should steer clear of meeting those with a compromised immune system for at least 10 days following the day their results were returned.
The overwhelming majority of people who catch Covid will not develop these serious symptoms, and severe cases can be prevented by getting vaccinated or receiving a booster jab to strengthen immunity. Those who have experienced the most recent strain of Covid have reported feeling poorly and confined to bed.
One social media user who fell ill in September said: "I had all them symptoms bar one earlier this week. I was in bed for 30+ hours knocked me on my a*** whatever it was."
Another wrote: "I have been really ill for about 6 weeks and the past 2 weeks on top of that been extra knocked out i.e feel like I have been heavily drinking, sniffles etc. Had a burning sensation at back of my mouth for 2 weeks very badly and since then mildly."
Despite the recent uptick in cases, officials have stressed that Covid infection levels across the UK remain broadly low.
Alex Allen, consultant epidemiologist at the UKHSA, said: "While Covid-19 activity has shown some recent increases, cases remain at low levels in the UK.
"UKHSA is monitoring all the data relating to Covid-19 variants in the UK and abroad, and we continue to publish our findings in our regular surveillance reports."
Stratus Covid has been circulating globally for some time, and was also linked to a separate outbreak in the US last year.
Despite being named after the US, experts believe it is unlikely to have originated there, with doctors suggesting it first took hold in Southeast Asia in 2025 before spreading across the rest of the globe.
Dr Magdalena Sobieszczyk, chief of the Division of Infectious Diseases at NewYork-Presbyterian/Columbia University Irving Medical Center, noted when the virus was doing the rounds last year that it is a particularly transmissible variant. She said: "Stratus has been around in Southeast Asia since January of this year, and came to the United States around the spring.
"We've been seeing an uptick since July, predominantly because it's a variant that can be transmitted easily and people were travelling a lot more, vaccine uptake has not been very high, and now many people are returning to school and their regular routines."
XFG is presently one of multiple Covid strains doing the rounds, with three others - BA. 3.2, NB.1.8. 1, and PQ.16.1. 1 - having also been identified by the World Health Organisation (WHO). They are spreading ahead of flu season, which generally kicks off around early October.
