The XFG variant — nicknamed Stratus, or 'American Covid' — has become the dominant Covid-19 strain in the UK, accounting for more than half of positive tests, according to the UK Health Security Agency. The recombinant lineage, a mix of the LF.7 and LP.8.1.2 Omicron sublineages, was first identified through genetic sequencing in the United States in January 2025.
According to BritBrief, UKHSA confirmed on October 8 that XFG has been circulating in Britain and internationally for around a year. The World Health Organization designated it a 'variant under monitoring' on June 25, 2025, a category for lineages with characteristics that may present an additional public health risk compared with other strains.
Dr. Alex Allen, a consultant epidemiologist at UKHSA, told reporters: 'The strains currently going around, including those known as XFG, are closely related to strains that have been with us for over a year, so this isn't something new.' The agency says there is no evidence that XFG causes more serious disease or death than other variants in circulation, and the additional global public health risk was assessed as low.
BritBrief reported that UKHSA data showed the rate of positive Covid tests in hospitals climbing from 5.9 percent to 7 percent in September, with London recording the sharpest regional rise. Sequenced samples show XFG lineages making up the majority of positives, with NB.1.8.1 ('Nimbus') and other JN.1 descendants also circulating.
UKHSA says this season's autumn Covid vaccines were updated to target XFG-related lineages and should remain effective. Officials are urging everyone eligible — people aged 75 and over, care home residents, and the severely immunosuppressed — to take up the offer before winter, when colder weather and indoor mixing typically drive respiratory viruses higher.
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