A new subvariant of the SARS-CoV-2 virus, identified as XFG and nicknamed “Stratus,” is gaining attention as the World Health Organization (WHO) designated it a “variant under monitoring” in late June. This designation indicates that XFG requires prioritized observation due to characteristics that could present a heightened risk compared to other circulating variants.
XFG is a recombinant variant, formed from the merging of LF.7 and LP.8.1.2, and is among the more than 1,000 subvariants of the Omicron variant. As of June 25, 2023, XFG was one of seven variants under monitoring, joining the ranks of NB.1.8.1, known as “Nimbus,” which was designated on May 23, 2023. Currently, Nimbus is the dominant subvariant globally, but Stratus is rapidly approaching its prevalence.
Understanding the Characteristics of XFG
Recombinant variants, like XFG, are denoted by an “X” at the beginning of their name. These variants arise when two subvariants exchange genetic material. While such recombinations occur frequently, they can become problematic if they lead to significant changes in the virus’s behavior, particularly in terms of immune evasion. XFG has four notable mutations in its spike protein, the component that allows the virus to attach to human cells. Preliminary laboratory studies indicate that XFG may exhibit nearly a two-fold reduction in antibody effectiveness compared to the LP.8.1.1 subvariant.
As of June 22, 2023, there were 1,648 XFG sequences reported from 38 countries in the GISAID database, the global repository for tracking COVID variants. This represented a substantial increase from just 7.4% of global sequences four weeks earlier to 22.7%. XFG’s rapid rise suggests it could soon surpass Nimbus as the leading variant.
According to data expert Mike Honey, countries with the highest detection rates of XFG include India, where it accounts for over 50% of cases, followed by Spain at 42%, and the United Kingdom and United States, where it constitutes more than 30% of reported cases. In Australia, as of June 29, 2023, NB.1.8.1 remains the dominant subvariant, making up 48.6% of sequences, while XFG represents approximately 5%.
Current Understanding and Concerns
With the emergence of a new variant, many people are understandably concerned about its severity and whether it causes different symptoms compared to previous variants. Current information about XFG is still developing, and while some reports suggest it may be linked to symptoms such as “hoarseness,” definitive conclusions cannot yet be drawn. Importantly, there is currently no evidence to suggest that XFG is associated with more severe illness or higher transmissibility than existing variants.
Vaccination remains a crucial component in combating COVID-19. The most recent vaccine update, which targets the JN.1 subvariant, became available in Australia in late 2024. Given that XFG descends from JN.1, existing vaccines are expected to maintain effectiveness against XFG, particularly in preventing symptomatic and severe illness.
Despite the ongoing evolution of SARS-CoV-2, vaccination rates, particularly among older populations, remain a concern. In Australia, only 32.3% of individuals aged 75 and over have received a COVID vaccine in the past six months, with even lower rates observed in younger age groups.
The WHO currently assesses the global risk posed by XFG as low, but monitoring continues. Public health recommendations remain the same: vaccination as recommended, early treatment with antivirals for those eligible, and measures to reduce transmission risk. These include wearing masks in crowded indoor settings and ensuring good air quality and ventilation to mitigate the spread of COVID-19 and other viral infections.
Paul Griffin, a principal investigator for clinical trials of eight COVID-19 vaccines and a director and medical advisory board member of the Immunisation Coalition, emphasizes the necessity for vigilance in the face of such emerging variants. As research progresses, the global health community will continue to adapt strategies to address the challenges posed by new variants like XFG.
