Stratus (XFG): What to Know About the New COVID Variant and Its Distinct Symptom

In the ever-evolving landscape of the COVID-19 pandemic, new variants of the SARS-CoV-2 virus continue to emerge and spread globally. The World Health Organization (WHO) recently added another variant, known officially as XFG and informally dubbed “Stratus,” to its list of variants under monitoring. This development underscores the persistent need for vigilance, genomic surveillance, and public understanding of how the virus continues to adapt.

Stratus is expected to circulate alongside other prevalent lineages, such as the now-dominant Nimbus variant, particularly throughout the northern hemisphere summer. While the WHO has initially assessed the risk to public health as low, the variant possesses distinct characteristics, including a notable symptom: hoarseness.

Understanding the Emergence of New Variants

Viruses, including SARS-CoV-2, constantly mutate as they replicate. Most mutations are harmless or even detrimental to the virus, but occasionally, a mutation or combination of mutations can give the virus an advantage, such as increased transmissibility, enhanced ability to evade the immune system, or changes in the severity of the disease it causes. When a lineage accumulates a set of mutations that significantly alter its characteristics, it can be classified as a new variant.

The WHO employs a system to track and classify SARS-CoV-2 variants based on their potential public health impact. Variants are categorized as Variants of Concern (VOC), Variants of Interest (VOI), or Variants Under Monitoring (VUM). This classification helps guide public health responses, research priorities, and risk assessments.

• Variants of Concern (VOC): These variants have demonstrated increased transmissibility, more severe disease (e.g., increased hospitalizations or deaths), significant reduction in neutralization by antibodies generated during previous infection or vaccination, reduced effectiveness of treatments or vaccines, or diagnostic detection failures. Examples include Alpha, Beta, Gamma, Delta, and Omicron.
• Variants of Interest (VOI): These variants have genetic changes that are predicted or known to affect virus characteristics (e.g., transmissibility, disease severity, immune escape, diagnostics, or therapeutics) and have been identified to cause significant community transmission or multiple COVID-19 clusters in multiple countries with increasing prevalence.
• Variants Under Monitoring (VUM): These variants have genetic changes that are suspected to affect virus characteristics with some indication of potential emerging risk, but the evidence is not yet clear. Stratus (XFG) currently falls into this category.

The classification of a variant can change as more data becomes available regarding its properties and global spread.

Introducing Stratus (XFG)

Stratus, or XFG, is a recombinant variant, meaning it arose from a person being infected with two different SARS-CoV-2 lineages simultaneously, leading to a new lineage that combines genetic material from both. Specifically, Stratus is a combination of the LF.7 and LP.8.1.2 lineages.

According to the WHO's initial assessment, Stratus exhibits “distinct mutational profiles in the spike protein” when compared to previously dominant variants like JN.1. The spike protein is particularly important because it is the part of the virus that binds to human cells and is the primary target of antibodies generated by vaccines and previous infections. Mutations in the spike protein can therefore significantly impact how easily the virus infects cells and how well the immune system recognizes and neutralizes it.

The WHO highlighted specific spike mutations at amino acids 478 and 487 in the Stratus variant. These particular mutations are associated with enhanced antibody avoidance. This means that antibodies developed from prior infection with other variants or from current vaccines might be less effective at preventing infection by Stratus, although they may still offer protection against severe disease.

The Distinct Symptom: Hoarseness

One of the most notable aspects of the Stratus variant, as reported by doctors and patients, is the prominence of hoarseness as a symptom. While many COVID-19 variants have shared a common set of symptoms including fever, cough, fatigue, muscle aches, and loss of taste or smell (though the latter became less common with Omicron and its descendants), Stratus appears to cause a particularly irritated or dry throat leading to hoarseness.

Reports from India, where Stratus was dominant throughout the spring, frequently mentioned hoarseness as a key indicator. Patients have also reported experiencing a dry cough and a general sore throat in addition to the more typical COVID-19 symptoms. This specific symptom profile can be a useful, though not definitive, indicator for clinicians and individuals suspecting a COVID-19 infection.

It is important to remember that symptom presentation can vary widely among individuals based on factors such as vaccination status, previous infection history, age, and overall health. However, the consistent reporting of hoarseness associated with Stratus infections provides valuable information for tracking and diagnosis.

Global Spread and Monitoring

Following its dominance in India during the spring, Stratus has begun to spread globally. Data from Gisaid, a global science initiative that provides open access to genomic data of influenza viruses and the SARS-CoV-2 virus, indicates a rapid increase in the variant's prevalence worldwide. In the last week of May, Stratus accounted for 22.7 percent of COVID-19 samples submitted to Gisaid, a significant jump from 7.4 percent just four weeks prior. These samples originated from 38 different countries, illustrating the variant's expanding geographical footprint.

The increase in detection is a direct result of ongoing global genomic surveillance efforts. Initiatives like Gisaid are crucial for tracking the emergence and spread of new variants, allowing public health authorities to monitor their characteristics and assess potential risks. This surveillance involves sequencing the genetic material of virus samples collected from infected individuals and sharing this data rapidly with the international scientific community.

The WHO's decision to classify Stratus as a Variant Under Monitoring is based on this accumulating data, indicating that the variant warrants close observation due to its increasing prevalence and mutational profile. Continued monitoring will involve tracking its growth rate relative to other circulating variants, assessing its impact on disease severity, and evaluating its potential to evade immune responses.

Public Health Implications and Vaccine Efficacy

The emergence of a new variant naturally raises questions about its potential impact on public health and the effectiveness of existing tools, particularly vaccines.

Based on currently available data, the WHO's risk assessment suggests that the risk to public health from Stratus is low. This assessment is likely based on observations regarding disease severity in areas where the variant has been prevalent. While the variant may be more adept at evading antibodies, there is no current evidence suggesting it causes more severe illness or a higher death rate compared to other circulating variants.

Furthermore, the WHO has stated that “The currently approved Covid-19 vaccines are expected to remain effective against this variant against symptomatic and severe disease.” This is a critical point. While mutations in the spike protein might reduce the vaccines' ability to prevent infection altogether (symptomatic or asymptomatic), the robust immune response generated by vaccination, particularly the cellular immunity component, is generally expected to continue providing strong protection against severe outcomes, hospitalization, and death.

Vaccine manufacturers and public health bodies like the WHO and national health agencies continuously monitor the effectiveness of current vaccines against emerging variants. Decisions regarding updating vaccine formulations are guided by ongoing surveillance data, including laboratory studies on variant neutralization and real-world effectiveness studies.

For instance, discussions around updating COVID-19 vaccines have been ongoing since the emergence of Omicron. Regulatory bodies like the FDA and EMA, in consultation with the WHO, periodically recommend updates to vaccine composition to better match circulating variants, aiming to improve protection against infection and transmission while maintaining strong protection against severe disease.

The ongoing need for updated vaccines is a testament to the virus's ability to evolve. As Wired has reported, the scientific community is also exploring next-generation vaccines that might offer broader protection against multiple variants or even other coronaviruses.

Comparing Stratus to Other Variants

Stratus is emerging at a time when the Nimbus variant (NB.1.8.1) has been dominant in many parts of the world. Comparing variants involves looking at their genetic makeup, transmissibility, immune evasion capabilities, and the clinical presentation of infections they cause.

While both Stratus and Nimbus are descendants of earlier Omicron lineages, their specific mutations differ. The enhanced antibody avoidance mutations in Stratus (at amino acids 478 and 487) are distinct and contribute to its ability to spread even among populations with high levels of immunity from vaccination or prior infection with other variants.

Symptomatically, while Nimbus also presents with typical cold-like symptoms, the emphasis on hoarseness appears to be a more characteristic feature of Stratus infections, based on current clinical observations. However, it's crucial to remember that symptom overlap exists between variants, and a definitive diagnosis requires testing.

The co-circulation of multiple variants like Stratus and Nimbus highlights the complex nature of the pandemic in its current phase. Public health efforts must account for the properties of the dominant variants circulating in a region.

Testing and Prevention in the Age of New Variants

The emergence of variants like Stratus reinforces the importance of continued testing. Knowing which variant is circulating helps public health authorities track its spread and characteristics. For individuals, testing remains the primary way to confirm a COVID-19 infection, regardless of the variant, allowing them to take appropriate isolation measures to prevent further transmission.

Rapid antigen tests and PCR tests are generally expected to detect the Stratus variant, as they target parts of the virus that are less likely to be affected by the specific mutations seen in this lineage. However, ongoing monitoring is necessary to ensure diagnostic tools remain effective.

Prevention strategies continue to be relevant. These include:

• Vaccination: Staying up-to-date with recommended COVID-19 vaccines and boosters remains the best defense against severe disease, hospitalization, and death, even with variants capable of some immune evasion.
• Masking: Wearing high-quality masks (such as N95, KN95, or KF94) in crowded indoor settings or when community transmission levels are high can significantly reduce the risk of inhaling or exhaling infectious particles.
• Ventilation: Improving ventilation in indoor spaces helps disperse viral particles, reducing the risk of transmission.
• Hand Hygiene: Regular hand washing or using hand sanitizer can help prevent the spread of respiratory viruses.
• Avoiding Crowds: Limiting close contact with others, especially indoors, when transmission rates are high.

These layered prevention strategies are effective against a range of respiratory viruses, including different SARS-CoV-2 variants.

The Role of Genomic Surveillance

The identification and monitoring of variants like Stratus are direct outcomes of robust genomic surveillance programs implemented globally. These programs involve collecting virus samples, sequencing their genetic code, and analyzing the data to identify new mutations and track the spread of different lineages.

Organizations like Gisaid and national public health laboratories play a critical role in this process. The rapid sharing of genomic data allows researchers and public health officials worldwide to stay informed about the evolutionary trajectory of the virus and anticipate potential challenges.

However, maintaining comprehensive genomic surveillance requires sustained investment and international cooperation. As TechCrunch has reported, funding for these crucial programs has faced challenges, raising concerns about potential blind spots in tracking future variants.

Robust surveillance is essential not only for identifying new variants but also for understanding their properties. Laboratory studies are conducted to assess how well antibodies neutralize the new variants and how efficiently they infect cells. Epidemiological studies track variant prevalence, growth rates, and associated disease severity in real-world populations.

This combination of genomic, laboratory, and epidemiological data provides the comprehensive picture needed to inform public health policies, vaccine strategies, and risk communication.

Living with an Evolving Virus

The emergence of Stratus is a reminder that SARS-CoV-2 is likely to continue evolving and circulating for the foreseeable future. Living with the virus means adapting to its changes and utilizing the tools available to mitigate its impact.

For individuals, this means staying informed about circulating variants, recognizing common symptoms (including new ones like prominent hoarseness with Stratus), and taking appropriate precautions based on personal risk tolerance and local transmission levels. Staying up-to-date with vaccination is a cornerstone of this approach.

For public health systems, it means maintaining strong surveillance capabilities, ensuring access to testing and treatment, and effectively communicating risk and guidance to the public. The experience gained over the past few years in tracking and responding to variants like Alpha, Delta, and Omicron provides a valuable foundation for managing the emergence of new lineages like Stratus.

While the initial assessment of Stratus indicates a low risk of increased severity, its ability to evade antibodies highlights the ongoing challenge of achieving durable immunity against infection. This underscores the importance of continued research into broader-acting vaccines and other preventative measures.

The informal name “Stratus,” evoking layers of clouds, perhaps inadvertently reflects the layered nature of the pandemic response needed: layers of immunity from vaccination and prior infection, combined with layers of public health measures and individual precautions.

As Stratus continues to spread, ongoing monitoring by organizations like the WHO and Gisaid will provide more detailed insights into its real-world impact. This data will be crucial for refining public health guidance and ensuring that the global community remains as prepared as possible for the virus's next move.

The story of Stratus is the latest chapter in the ongoing narrative of human interaction with a novel pathogen. It highlights the dynamic nature of viruses and the critical role of science, surveillance, and public health action in navigating a world where infectious diseases continue to evolve.

Staying informed through credible sources, understanding the current risk landscape, and utilizing available tools like vaccination and testing are key steps for individuals navigating the continued presence of COVID-19 and its emerging variants.

The global health community remains focused on tracking variants, assessing risks, and guiding responses. The information gathered on Stratus will contribute to the collective understanding of SARS-CoV-2 evolution and inform future strategies for pandemic preparedness and response.

For further information on variant tracking and public health guidance, consult resources from the World Health Organization and national health agencies.

Conclusion

The emergence of the Stratus (XFG) variant, characterized by symptoms like hoarseness and possessing mutations that enhance antibody evasion, is a significant development in the ongoing COVID-19 pandemic. While currently classified as a Variant Under Monitoring with an initial low-risk assessment for severe disease, its rapid global spread necessitates continued vigilance and surveillance.

The situation with Stratus underscores the importance of global genomic surveillance initiatives like Gisaid and the critical role of organizations like the WHO in monitoring and classifying new threats. It also reinforces the value of existing public health tools, particularly vaccination, which is expected to remain effective against severe outcomes, and the continued relevance of testing and layered prevention strategies.

As the virus continues to evolve, staying informed, understanding the characteristics of circulating variants, and utilizing available protective measures remain essential for individuals and communities worldwide. The story of Stratus is a reminder that the pandemic is not over, but the tools and knowledge developed over the past few years provide a strong foundation for managing its ongoing challenges.