A new COVID-19 variant, known as XFG or “Stratus,” is surging across the United States, swiftly becoming the third-most common strain of the summer and raising concerns among health authorities. The fast-spreading variant, first detected in Southeast Asia in January, has also been reported in several European countries.
According to the Centers for Disease Control and Prevention (CDC), XFG accounted for virtually none of the cases in the US until April, when it registered at 2 per cent. By late May, it had climbed to 6 per cent, before doubling to 11 per cent in early June. Just weeks later, it reached 14 per cent, a sharp and steady rise.
High or very high case levels have been reported in states including Alabama, Alaska, California, Delaware, Florida, Hawaii, Kentucky, Louisiana, and Texas. Meanwhile, infections are also on the rise in other parts of the country, such as New York, Pennsylvania, North Carolina, Virginia, and Washington.
Another strain, NB.1.8.1, nicknamed “Nimbus”, is also circulating widely in the US, with reports suggesting it often causes a severe sore throat.
What We Know About XFG
The World Health Organization (WHO) describes XFG as a recombinant variant, formed from lineages LF.7 and LP.8.1.2. The earliest known sample was collected on January 27, 2025. In June, the WHO classified it as a “variant under monitoring” due to its increasing global spread.
Experts say the virus that causes COVID-19, SARS-CoV-2, continues to evolve, picking up mutations that may help it evade immune defences. Professor Subhash Verma, a microbiology and immunology expert at the University of Nevada, Reno, told USA Today that XFG’s mutations could potentially improve its ability to bypass immune responses.
However, the WHO currently assesses the public health risk posed by XFG as low, noting there is no evidence it causes more severe illness or markedly different symptoms compared to earlier Omicron strains. Current COVID-19 vaccines are still expected to protect against both symptomatic and severe disease caused by this variant.
Symptoms to Watch For
The CDC lists the following as common COVID-19 symptoms, which apply to infections caused by XFG:
- Fever or chills
- Cough
- Shortness of breath or difficulty breathing
- Sore throat
- Congestion or runny nose
- Loss of taste or smell
- Fatigue
- Muscle or body aches
- Headache
- Nausea or vomiting
With XFG’s presence growing, health officials continue to urge vaccination, mask use in crowded spaces, and testing for those experiencing symptoms.
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