American Covid Strain: XFG ‘Stratus’ Behind Rise In England As London Hospital Admissions Jump

The so-called “American Covid strain” is attracting fresh attention in Britain after COVID-19 hospital admissions rose sharply in England, with the latest official figures showing an especially notable increase in London.

The strain at the centre of the coverage is XFG, commonly nicknamed “Stratus”. “American Covid” is not an official name used by the World Health Organisation (WHO) or the UK Health Security Agency (UKHSA), and the label should not be taken to mean that the variant originated in the United States.

Instead, XFG is one of a number of Omicron-descended SARS-CoV-2 lineages that have circulated internationally. WHO continues to list XFG as a variant under monitoring, with its earliest documented samples dating to January 2025.

Interest in the term has surged in Britain as new reporting highlighted an increase in COVID activity. Google Trends data on 3 October showed “american covid strain” among the UK’s rapidly rising search terms, following widespread coverage of the latest hospital figures.

The important context, however, is that the rise is coming from relatively low levels.

UKHSA’s latest national flu and COVID-19 surveillance report, covering data up to 20 September, said COVID-19 activity in England had increased but remained at a low level.

Hospital PCR positivity rose from 5.9% to 7.0% in a week, while the overall weekly COVID-19 hospital admission rate increased from 0.81 to 1.20 admissions per 100,000 people.

That represents a rise of roughly 48% in a week, although UKHSA still classified the hospital admission indicator as being at baseline level.

London recorded the highest regional hospital admission rate.

The capital’s rate climbed from 0.95 to 1.70 admissions per 100,000, an increase of almost 79% from the previous week.

The rise was particularly pronounced among the oldest patients nationally. For people aged 85 and over, the hospital admission rate increased from 7.08 to 12.43 per 100,000.

Those figures explain why the latest increase is being watched closely as Britain moves deeper into autumn, even though experts are not describing the current situation as comparable with the major COVID waves experienced during the pandemic.

Alex Allen, a consultant epidemiologist at UKHSA, told The Independent that while recent COVID activity had increased, “cases remain at low levels in the UK.” UKHSA continues to monitor variants circulating both domestically and internationally.

Dr Matthew Siggins, lecturer in immunity and infection biology at the University of Surrey, similarly said there was currently “no evidence” that circulating UK variants were producing more severe disease than other recent variants.

He cautioned, however, that COVID can still cause serious illness among people who are at greatest risk.

The increase also comes at a time of year when respiratory infections normally begin to receive more attention.

Dr Siggins said rising COVID activity was not unexpected as colder weather approaches. Waning immunity, changing circulating variants and more indoor social contact can all influence transmission.

Professor Paul Hunter, professor of medicine at the University of East Anglia, also pointed out that reported infections and hospitalisations remain lower than at the equivalent point last year.

What Is the American Covid Strain XFG?

XFG is a recombinant SARS-CoV-2 lineage, meaning it developed through genetic material from related viral lineages combining.

WHO began formally monitoring XFG in June 2025 and still lists it among circulating variants under monitoring.

Although “Stratus” has become a widely used nickname, and British news coverage has increasingly called it “American Covid”, neither description replaces its scientific lineage designation, XFG.

The “American” label can also create an inaccurate impression about where the variant came from. WHO records the earliest documented XFG samples from 27 January 2025, but its official designation does not describe the strain as American.

The variant subsequently circulated internationally, including in the United States, Britain and other countries.

Current English sequencing data shows that XFG’s wider family remains significant.

Among sequenced COVID-positive samples collected between 17 and 30 August, 46.2% were XFG.23.1.3, while another 12.8% were XFG.14.8 and 5.1% were classified directly as XFG.

Taken together, those named XFG lineages accounted for around 64% of the sequenced samples in that reporting period.

UKHSA stresses that recent sequencing numbers are relatively small and that the estimates should therefore be interpreted cautiously.

There is also no current evidence that XFG is producing more severe illness simply because it has become prominent.

WHO reported earlier in 2026 that none of the SARS-CoV-2 variants then being monitored had shown evidence of an increased overall public-health risk.

That distinction matters.

A variant can become more common because it spreads efficiently or has advantages over competing lineages without necessarily causing more severe disease in an individual patient.

What Symptoms Are Doctors Seeing?

The symptoms being linked with the current XFG wave remain broadly similar to symptoms seen with other recent COVID variants.

They can include:

• Sore throat
• Cough
• High temperature or fever
• Headache
• Runny or blocked nose
• Fatigue or exhaustion
• Muscle and body aches
• Changes to smell or taste
• Gastrointestinal symptoms in some patients

London GP Dr Renée Hoenderkamp said she had noticed more patients presenting with sore throats, headaches, runny noses and fatigue during recent weeks.

Describing the current pattern, she said it was “very flu-like”, making it difficult for patients to distinguish COVID from other respiratory infections purely from symptoms.

That assessment broadly matches NHS guidance.

The NHS lists high temperature, continuous cough, tiredness, headache, sore throat, blocked or runny nose, aching muscles, shortness of breath, diarrhoea and nausea among possible COVID symptoms.

It also makes clear that COVID symptoms can closely resemble colds, influenza and other respiratory infections.

This means symptoms alone cannot reliably establish whether somebody has XFG, another COVID lineage, influenza or another seasonal virus.

Disease severity can also differ substantially from one person to another.

Professor Emma Wall, clinical professor of infectious diseases at Queen Mary University of London, said some patients can be “floored by an infection while others remain asymptomatic”, highlighting the wide variation in individual immune responses to the virus.

Age, immune status, previous infection, vaccination history and existing medical conditions can all influence how seriously someone becomes ill.

For most people, the latest rise therefore does not signal a return to the emergency conditions experienced earlier in the pandemic.

For older and immunosuppressed people, however, the risk of serious disease remains more significant.

That is reflected in England’s autumn 2026 COVID vaccination programme.

Vaccination is being offered to adults aged 75 and over, residents of care homes for older adults and people aged six months and above who are immunosuppressed. The programme is specifically targeted at people considered most vulnerable to serious COVID outcomes.

The timing has become particularly relevant as London’s hospital admission rate has risen faster than the national figure.

A one-week percentage increase of almost 80% may sound dramatic, but the starting rate was low.

Moving from 0.95 to 1.70 admissions per 100,000 therefore represents a substantial proportional rise without indicating hospital pressure anywhere close to pandemic-era levels.

UKHSA’s classification remains the clearest context:

Overall COVID activity was low and hospital admissions were at baseline levels in the latest report, even though both were increasing.

People who develop respiratory symptoms alongside a high temperature, or who feel too unwell to carry out their normal activities, are advised by the NHS to try to stay at home and avoid contact with other people until they feel better.

Adults who choose to take a COVID test and receive a positive result are advised to try to stay home and avoid contact with others for five days after the test.

People are also advised to avoid meeting anyone particularly vulnerable to serious infection for 10 days after a positive test.

For London, the next surveillance reports will be important in establishing whether the current increase develops into a sustained autumn wave or proves to be a short-lived rise.

For now, the evidence supports a more measured picture than the “American Covid” nickname may suggest:

XFG and its descendants are circulating prominently, hospital admissions have increased and London has recorded the sharpest regional rise, but official surveillance continues to describe overall COVID activity as low, with no evidence that XFG is causing more severe disease than other currently circulating variants.