A new subvariant of SARS-CoV-2, identified as XFG and informally referred to as “Stratus,” has been designated a “variant under monitoring” by the World Health Organization (WHO). This classification was made in late June 2023, indicating that XFG warrants prioritized attention due to its potential implications for public health. XFG is a recombinant subvariant of the Omicron variant, which has seen an explosion of over 1,000 subvariants since its emergence.
Understanding the designation of a “variant under monitoring” is crucial. It signifies that XFG may present additional risks compared to other circulating variants. As of June 25, 2023, XFG was among seven variants under this classification. The previous addition was NB.1.8.1, nicknamed “Nimbus,” which received the same designation on May 23, 2023. Notably, both “Nimbus” and “Stratus” draw their names from types of clouds, reflecting the scientific community’s approach to categorizing these variants.
Characteristics of XFG
XFG is classified as a recombinant variant, created from the genetic material of two other subvariants, LF.7 and LP.8.1.2. This process of recombination can lead to new variants that may display altered properties, particularly in terms of immune evasion. Such changes could compromise the effectiveness of immunity gained through previous infections or vaccinations, thereby increasing susceptibility within the population.
XFG has exhibited four key mutations in its spike protein, which is essential for the virus’s ability to attach to human cells. Preliminary laboratory studies suggest that antibodies may be nearly two times less effective at blocking XFG compared to the LP.8.1.1 subvariant.
As of June 22, 2023, a total of 1,648 sequences of XFG were reported to GISAID, the global database tracking variant prevalence, across 38 countries. This represents 22.7% of the total sequences available, a significant increase from 7.4% just four weeks earlier. The rapid rise of XFG indicates it may soon surpass NB.1.8.1, which was at 24.9%.
According to data expert Mike Honey, the countries with the highest detection rates of XFG include India, where it accounts for over 50% of cases, followed by Spain at 42%, and both the United Kingdom and the United States, where it represents more than 30% of reported cases. In Australia, the situation is slightly different; as of June 29, 2023, NB.1.8.1 remains the dominant subvariant, constituting 48.6% of sequences. The latest report from Australia’s genomic surveillance platform revealed 24 XFG sequences, with 12 collected in the last 28 days, suggesting it currently makes up about 5% of local cases.
Public Health Implications
With the emergence of a new variant, public concern often centers on whether the variant leads to more severe symptoms or different health outcomes compared to its predecessors. As of now, it remains unclear if XFG is associated with increased severity or new symptoms. Some reports indicate a potential link to symptoms like “hoarseness” or a scratchy voice, but further research is needed to substantiate these claims.
Importantly, there is currently no evidence suggesting that XFG causes more severe illness than existing variants or that it possesses significantly higher transmissibility.
Vaccination remains a critical tool in combating COVID-19. The most recent updates to COVID vaccines, which target the JN.1 subvariant, became available in Australia in late 2024. XFG is a descendant of this subvariant, and initial evidence indicates that existing vaccines are likely to remain effective against XFG, particularly in preventing symptomatic and severe disease. Given the evolving nature of SARS-CoV-2, health authorities are continuing to recommend vaccinations, especially for high-risk groups.
In Australia, vaccination rates, especially among older adults, have been a concern. As of now, only 32.3% of individuals aged 75 years and older have received a vaccine in the past six months, with much lower rates among younger populations.
Despite the emergence of XFG, the WHO currently assesses the global risk posed by this subvariant as low. Public health recommendations remain unchanged, focusing on vaccination, early antiviral treatment for eligible individuals, and implementing measures to reduce transmission risks, such as wearing masks in crowded indoor settings and improving ventilation.
Experts like Paul Griffin, who has led clinical trials for COVID-19 vaccines, continue to emphasize the importance of vaccination and public health measures in managing the ongoing pandemic. The landscape of COVID-19 continues to change, requiring vigilance and adaptability from both health agencies and the public.
