XFG, nicknamed "Stratus" and dubbed "American Covid" in UK headlines, is an Omicron recombinant that UK health data show became the dominant circulating lineage by late summer 2026. UKHSA figures recorded a near-50% weekly rise in English hospital admissions as the variant spread, though the World Health Organization rates its global public-health risk as low.
Searches for "American Covid" and "XFG" rose in the UK in late September and early October 2026 after official surveillance data showed hospital admissions climbing for the first time since the summer. The variant driving the increase, XFG, has circulated globally since early 2025 but only became the majority strain in England's sequenced samples in recent weeks.
What is XFG?
XFG is a recombinant of two earlier Omicron sub-lineages, LF.7 and LP.8.1.2, according to the World Health Organization's variant classification, reported by health-news outlet CIDRAP. The earliest known sample was collected on 27 January 2025, and the WHO added XFG to its list of "variants under monitoring" on 25 June 2025. It has picked up the informal name "Stratus"; because it became the dominant strain in the United States, some UK and international coverage has also labelled it "American Covid," according to WION.
By 22 June 2025, XFG sequences had been reported from 38 countries, representing 22.7% of globally shared sequences at that point, according to WHO figures cited by both CIDRAP and The Conversation. The Conversation, drawing on the same WHO assessment, reported detection rates above 30% in the UK and US, over 50% in India, and 42% in Spain at that time. By the UK's week-39 surveillance report (covering sequences from 17–30 August 2026), published by the UK Health Security Agency (UKHSA), two XFG sub-lineages — XFG.23.1.3 and XFG.14.8 — together accounted for 59% of sequenced English cases, ahead of NB.1.8.1 (12.8%) and the older JN.1 lineage (7.7%).
Symptoms linked to XFG
The WHO assessment, as summarised by both CIDRAP and The Conversation, states there is no sign that XFG causes more severe illness than other circulating variants. Reported symptoms overlap with earlier Omicron strains: fever, cough, runny nose, headache and fatigue, according to coverage summarised by news outlet WION. Some reports have described hoarseness or a "scratchy" voice in XFG cases and, separately, gastrointestinal symptoms, but The Conversation and WHO's own assessment caution that more data is needed before any symptom is confirmed as distinctive to this variant.
The WHO evaluation also found a roughly 1.9-fold reduction in antibody neutralisation against XFG compared with the earlier LP.8.1.1 lineage in laboratory studies, linked to two mutations in the virus's spike protein. Despite this, the WHO states that currently approved COVID-19 vaccines are expected to remain effective against XFG, particularly in preventing symptomatic and severe disease.
Why the UK is seeing an autumn surge
UKHSA's national flu and COVID-19 surveillance report for week 39 (data to 24 September 2026) recorded a rise in the overall weekly hospital admission rate in England to 1.20 per 100,000 people, up from 0.81 the previous week — an increase of close to 50%. London showed the sharpest regional rise, from 0.95 to 1.70 admissions per 100,000. Among people aged 85 and over, the rate rose from 7.08 to 12.43 per 100,000. The same report put hospital PCR positivity at 7.0% for the week ending 20 September, up from 5.9% the week before, while community GP-swab positivity held closer to steady, at 7.9% versus 7.5%. UKHSA's own wording describes the trend as COVID-19 activity that "increased and is circulating at low levels" overall, and WION's reporting notes that medical experts cautioned the rise did not necessarily indicate a major problem, consistent with typical seasonal patterns.
UKHSA England COVID-19 indicators, week 39 2026 vs previous week
Indicator
Previous week
Week 39 (to 24 Sept 2026)
Overall hospital admissions (per 100,000)
0.81
1.20
London hospital admissions (per 100,000)
0.95
1.70
Age 85+ hospital admissions (per 100,000)
7.08
12.43
Hospital PCR positivity
5.9%
7.0%
GP swab positivity
7.5%
7.9%
What health authorities are advising
UKHSA's published advice, summarised in WION's reporting, continues to focus on people with symptoms avoiding contact with others, particularly anyone at higher risk of severe illness, while they have a high temperature or feel unwell enough that it affects normal activities. WION's coverage of the current guidance notes that a cough alone does not require isolation under present UK rules, though wearing a mask around others is suggested. Medical commentary cited by WION describes the current season as involving a mix of several respiratory illnesses circulating together, rather than COVID-19 alone.
The WHO's formal risk evaluation, as reported by CIDRAP, rates XFG's additional public-health risk as low at the global level, citing a moderate growth advantage over other lineages combined with what it assesses as limited immune escape. The WHO assessment also notes that confidence in some of these judgements remains low because of the variant's recent emergence and limited volumes of genomic sequencing in some regions.
So far there is no sign that infections are more severe.
— WHO risk assessment, as cited by CIDRAP
Questions
Is XFG more dangerous than earlier COVID variants?
No. The World Health Organization's assessment, reported by CIDRAP, states there is no evidence that XFG causes more severe illness or higher mortality than other variants currently circulating.
What are the main symptoms of the XFG ('Stratus') variant?
Reported symptoms include fever, cough, runny nose, headache and fatigue, similar to earlier Omicron strains. Some reports mention hoarseness or gastrointestinal symptoms, but WHO-linked assessments say more data is needed before treating these as distinctive to XFG.
Why is it called 'American Covid' if XFG spread worldwide?
UK and international headlines have used the term because XFG became the dominant strain in the United States, where WHO figures cited by CIDRAP showed it made up 14% of sequenced samples by 21 June 2025.
Do COVID vaccines still work against XFG?
The WHO states that currently approved vaccines are expected to remain effective against XFG, particularly in preventing symptomatic and severe disease, despite a measured reduction in antibody neutralisation in laboratory studies.
Should I isolate if I test positive for COVID this autumn?
UK guidance summarised by WION advises avoiding contact with others while you have a high temperature or feel too unwell for normal activities, especially around people at higher risk; a cough alone is not treated as a reason to isolate, though masking is suggested.
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