A new COVID-19 lineage called Stratus, also referred to as XFG and XFG.3, is showing increased prevalence in the UK, according to the UK Health Security Agency (UKHSA). While WHO classifies it as a Variant Under Monitoring with low additional public health risk, recent media reports have noted a hoarse or croaky voice as a commonly observed symptom.
What Is Stratus (XFG)?
“Stratus” is the media nickname for a group of Omicron-descendant lineages, primarily XFG and XFG.3. These lineages have shown rapid growth in recent sequencing reports from England and other UK regions. The World Health Organization (WHO) designated XFG as a Variant Under Monitoring on 25 June 2025, assessing its added risk to public health as low based on current evidence.
How Common Is It?
According to UKHSA surveillance, XFG and XFG.3 now make up a significant proportion of sequenced cases in England. Recent reports indicate that XFG alone accounts for roughly one-third of typed samples, with XFG.3 at a similar level. UKHSA notes that numbers are influenced by sequencing coverage and reporting delays, but both lineages have been prominent from late summer into early autumn.
Symptoms Observed
The core COVID-19 symptoms, fever, cough, fatigue, sore throat, and congestion, remain largely unchanged. Anecdotal reports from the media indicate that some individuals experience a hoarse or croaky voice during infection. However, UKHSA emphasizes that this is not associated with increased severity and remains observational.
Severity and Risk
Current data show that XFG and XFG.3 do not cause more severe illness than other recent Omicron variants. Hospitals and public health authorities continue to monitor admissions and genomic sequencing to detect any shifts in severity. The WHO confirms that, on a global scale, XFG is considered low-risk.
Vaccines and Protection
Existing COVID-19 vaccines are expected to remain effective against symptomatic and severe disease caused by XFG. Ongoing laboratory studies are refining our understanding of immune escape, but UKHSA advises keeping vaccinations up to date, particularly seasonal boosters, as the best protection heading into autumn and winter.
Practical Guidance
To reduce the risk of infection:
- Stay home if you are unwell.
- Ensure good ventilation indoors.
- Consider testing if symptomatic, especially around vulnerable people.
- Seek medical advice for persistent or worsening symptoms.
High-risk groups include older adults, pregnant individuals, and immunocompromised people, who should remain extra cautious.
Stay informed by checking UKHSA weekly surveillance reports and trusted public health updates for changes in variant prevalence and vaccine guidance.
