As the world continues to navigate the challenges posed by COVID-19, a new subvariant of the virus has emerged, drawing attention from global health authorities. Known as XFG and nicknamed “Stratus,” this subvariant has been classified as a “variant under monitoring” by the World Health Organization (WHO) since late June. XFG is a descendant of the Omicron variant, which has spawned over 1,000 subvariants to date.
The designation of “variant under monitoring” indicates that XFG possesses characteristics that may pose additional threats compared to other circulating variants. As of June 25, XFG was one of seven such variants under scrutiny, with NB.1.8.1, or “Nimbus,” being the most recent addition prior to XFG. Both “Nimbus” and “Stratus” draw their names from types of clouds, reflecting the ongoing challenge of tracking and naming emerging variants.
The Genetic Makeup of XFG
XFG is a recombinant variant, meaning it has emerged from the genetic material of two other subvariants, LF.7 and LP.8.1.2. Recombinants are identified by an “X” at the beginning of their name. While recombination is a common occurrence with SARS-CoV-2, it becomes concerning when the resulting subvariant exhibits properties that could exacerbate the pandemic. This often involves immune evasion, where the virus appears different enough that previous infection or vaccination offers reduced protection.
Notably, XFG has four key mutations in the spike protein, which allows the virus to attach to human cells. These mutations are suspected to enhance the virus’s ability to evade certain antibodies. Early laboratory studies suggest a nearly two-fold reduction in antibody effectiveness against XFG compared to LP.8.1.1.
Global Spread and Impact
The earliest sample of XFG was collected on January 27. By June 22, 1,648 XFG sequences had been submitted to GISAID, a global database tracking the prevalence of different variants. This represented 22.7% of globally available sequences, a significant rise from 7.4% just four weeks earlier. The rapid increase in XFG’s prevalence suggests it may soon surpass NB.1.8.1, which accounted for 24.9% of sequences at the time.
According to Australian data expert Mike Honey, countries with the highest detection rates of XFG as of mid-June include India (over 50%), Spain (42%), and both the United Kingdom and the United States, where it comprises over 30% of cases. In Australia, NB.1.8.1 remained dominant at 48.6% of sequences, but XFG was gaining ground, making up approximately 5% of sequences.
Public Health Implications
As with any new subvariant, questions arise about XFG’s severity and symptomatology. Current information does not indicate that XFG causes more severe illness or is more transmissible than other variants. However, some reports suggest it may be associated with symptoms like hoarseness, though more data is needed to confirm this.
Vaccines remain a critical tool in combating COVID-19. While the virus’s frequent mutations necessitate updates to vaccines, current vaccines are expected to remain effective against XFG, particularly in preventing symptomatic and severe disease. The latest vaccine update, targeting the JN.1 subvariant, became available in Australia in late 2024. XFG, as a descendant of JN.1, should be covered by this update.
Despite these assurances, vaccine uptake remains a challenge. In Australia, only 32.3% of people aged 75 and over have received a vaccine in the past six months, with even lower rates in younger age groups. The WHO currently assesses the global risk posed by XFG as low, but emphasizes the importance of continued vaccination and early antiviral treatment for eligible individuals.
Looking Ahead
As the situation with XFG evolves, public health measures such as wearing masks in crowded indoor settings and improving air quality remain vital. These strategies not only help mitigate the spread of COVID-19 but also protect against other viral infections.
Paul Griffin, a principal investigator for clinical trials of eight COVID-19 vaccines and a member of medical advisory boards, underscores the importance of maintaining vigilance and preparedness as the virus continues to evolve. The global community must remain alert to new developments and ready to adapt strategies as needed.
