A new subvariant of the SARS-CoV-2 virus, named XFG and informally referred to as “Stratus,” has been designated a “variant under monitoring” by the World Health Organization (WHO) as of late June 2023. This designation indicates that XFG requires closer observation due to its potential impact on public health. As a subvariant of Omicron, XFG is part of an extensive lineage, with more than 1,000 variants having been identified since the onset of the pandemic.
As of June 25, XFG was among seven variants under monitoring. The previous addition was the NB.1.8.1 subvariant, known as “Nimbus,” which the WHO classified on May 23. Both names are derived from types of clouds, reflecting a thematic approach to naming variants. Currently, Nimbus is the dominant subvariant globally, but XFG’s rapid rise suggests it could soon take its place.
Understanding the XFG Subvariant
XFG is classified as a recombinant variant, meaning it has emerged from the combination of genetic material from two existing subvariants, LF.7 and LP.8.1.2. Such recombination events are not uncommon with SARS-CoV-2, but they can lead to variants that may evade immune protection from previous infections or vaccinations. This immune evasion is concerning as it can increase the virus’s transmissibility and lead to new waves of infections.
Preliminary laboratory studies have indicated that antibodies may be less effective against XFG, with an estimated nearly two-fold reduction in neutralization compared to its predecessor, LP.8.1.1. XFG features four significant mutations in its spike protein, which aids the virus in attaching to human cells. These mutations are thought to enhance the virus’s ability to evade immune responses.
As of June 22, there were 1,648 XFG sequences submitted to GISAID, a global database that monitors variant prevalence, across 38 countries. This figure represents 22.7% of the global sequences available at that time, a considerable increase from 7.4% just four weeks earlier. XFG is rapidly gaining ground, poised to become a dominant variant, especially given the decline of NB.1.8.1’s prevalence.
According to data expert Mike Honey, the highest detection rates of XFG are in India, where it constitutes over 50% of cases, followed by Spain at 42%, and both the United Kingdom and the United States, where it accounts for more than 30%. In Australia, as of June 29, NB.1.8.1 remained the leading subvariant, comprising 48.6% of sequences, while XFG represented approximately 5%.
Potential Impacts and Ongoing Research
With the emergence of XFG, many are questioning whether this subvariant is associated with more severe disease or different symptoms compared to earlier variants. Currently, there is no conclusive evidence suggesting that XFG results in more severe illness or increased transmissibility. Some early reports indicate a possible link between XFG and symptoms like “hoarseness,” but further investigation is necessary to establish any significant correlation.
Vaccination remains a critical line of defense against COVID-19. Recent updates to COVID vaccines, including one targeting the JN.1 subvariant, have been made available in Australia since late 2024. XFG, being a descendant of JN.1, indicates that existing vaccines are likely to retain effectiveness against it, particularly in preventing symptomatic and severe disease. Nonetheless, the evolving nature of SARS-CoV-2 necessitates ongoing updates to vaccines to keep pace with its mutations.
Despite the potential threats posed by XFG, the WHO currently assesses the global risk of this subvariant as low. Recommended measures to mitigate COVID transmission remain unchanged, emphasizing the importance of vaccination, early administration of antiviral treatments for those eligible, and continued public health measures such as wearing masks in crowded spaces and improving indoor air quality.
Paul Griffin, a noted expert in COVID-19 vaccine trials, underscores the importance of monitoring XFG closely while highlighting that vaccination rates need improvement. In Australia, vaccine uptake among older populations has improved but still lingers at only 32.3% for those aged 75 and over in the past six months, with rates significantly lower in younger demographics.
As the global community continues to navigate the challenges posed by COVID-19, vigilance and adaptability in public health responses will be critical in managing the impact of emerging variants like XFG.
