As the world continues to grapple with the ever-evolving landscape of Covid-19, a new variant known as 'Stratus' has rapidly emerged as a dominant strain, particularly in the United Kingdom. Scientifically referred to as XFG, and including a spin-off variant XFG.3, Stratus has sparked concern among health experts due to its swift spread and unique characteristics. Yet, despite its accelerated transmission, authorities emphasize that this variant does not currently pose a greater health risk than previous strains.
The World Health Organization (WHO) recently reported a significant rise in Stratus cases globally, noting that the variant accounted for just 7% of Covid-19 infections worldwide in May 2025 but surged to 23% by June 1, 2025. In England, the UK Health Security Agency (UKHSA) data revealed that Stratus jumped from representing 10% of Covid cases in May to almost 40% by mid-June. Between May 26 and June 8, 28.9% of cases were classified as XFG.3 and 11.4% as XFG, illustrating the rapid proliferation of this recombinant strain.
Stratus is a so-called 'Frankenstein' or recombinant variant, meaning it originated when a person was simultaneously infected with two different Covid strains, which then combined to form a new hybrid variant. This recombinant nature is a hallmark of several recent variants, including the Omicron lineage and its offshoots such as NB.1.8.1, nicknamed 'Nimbus,' and hybrid forms like 'Deltacron.' These 'Frankenstein' variants are characterized by a high number of mutations, particularly in the spike protein—the part of the virus responsible for entering human cells.
Professor Lawrence Young, a virologist at Warwick University, explained to MailOnline that the increased competitiveness of Stratus and its spin-off is likely due to new spike mutations that help the virus evade immune responses. "Given that immunity to Covid is waning in the population due to a decline in uptake of the spring booster jab and the reduction of Covid infections in recent months, more people will be susceptible to infection with XFG and XFG.3," he said. He warned that this could lead to a new wave of infections, though the extent remains difficult to predict.
Despite its rapid spread, the WHO has classified Stratus as a 'variant under monitoring' and assessed its overall risk to global public health as low. The agency pointed out that current data do not indicate that Stratus leads to more severe illness or deaths than other variants in circulation. Dr. Alex Allen, consultant epidemiologist at UKHSA, echoed this sentiment, stating, "There is no evidence to suggest that the XFG and XFG.3 variants cause more severe disease than previous variants, or that the vaccines in current use will be less effective against them." The UKHSA continues to monitor all available data related to SARS-CoV-2 variants, publishing regular surveillance reports.
One area of concern, however, is the variant's ability to evade immunity. A study published in The Lancet Infectious Diseases highlighted that XFG has four key mutations and displays "strong immune evasion," although it appears less effective at attaching to the ACE2 receptor, the virus's entry point into human cells. Dr. Kaywaan Khan, a Harley Street GP and founder of Hannah London Clinic, explained in an interview with Cosmopolitan UK that Stratus's mutations in the spike protein could help it evade antibodies developed from prior infections or vaccinations. Nevertheless, he emphasized that Stratus does not seem to result in more severe illness, hospitalizations, or deaths compared to earlier Omicron variants.
Symptomatically, Stratus generally resembles previous Covid strains, but with one distinctive feature: hoarseness. Dr. Khan noted, "One of the most noticeable symptoms of the Stratus variant is hoarseness, which includes a scratchy or raspy voice." This symptom has also been observed by doctors in India, where Stratus is dominant. The NHS lists common Covid symptoms that continue to apply, including a high temperature or shivering, a new continuous cough, loss or change to smell or taste, shortness of breath, fatigue, aching body, headache, sore throat, blocked or runny nose, loss of appetite, diarrhoea, and feeling or being sick.
Testing remains crucial in identifying cases, especially since Stratus is highly contagious. Dr. Khan advised that individuals who test positive should stay home and isolate to prevent further spread. The NHS also recommends covering the mouth and nose with a mask, avoiding crowded indoor spaces, and informing close contacts and healthcare providers about any infection.
While the new variant's spread is cause for vigilance, public health officials stress the importance of vaccination. Current Covid vaccines are expected to remain effective against Stratus in preventing symptomatic and severe disease. This is particularly vital as immunity wanes in the population due to reduced booster uptake and fewer recent infections. Vulnerable groups, including older adults, young children, and immunocompromised individuals, remain at higher risk of severe outcomes and should continue to take precautions.
In the UK, recent data suggest a decline in overall Covid activity. The UKHSA reported that Covid-19 activity decreased across most indicators in the week ending June 29, 2025, reaching baseline levels. Hospital admissions dropped from 1.46 to 0.99 per 100,000 people, and the percentage of positive tests in GP surgeries fell from 8.8% to 7.8%. Meanwhile, the Nimbus variant, characterized by a painful 'razor blade' sore throat and swollen neck glands, is becoming less prevalent, accounting for just over 7% of cases.
As the virus continues to mutate, the emergence of variants like Stratus underscores the dynamic nature of the pandemic. The term 'Frankenstein variant' aptly captures the patchwork genetic makeup of these strains, which may confer advantages in transmission and immune evasion. Yet, current evidence suggests that while these variants spread quickly, they do not necessarily cause more severe illness.
Ultimately, the global health community remains vigilant but cautiously optimistic. Continued surveillance, vaccination efforts, and public health measures are key to managing the evolving threat. As Professor Young succinctly put it, "Vaccination remains a potent shield against severe outcomes and hospital admissions," reminding us that even as the virus changes, our best defenses remain largely intact.
