Chloe Ramirez
As of September 2025, the XFG COVID-19 variant, also known as Stratus, is spreading rapidly in the US. The World Health Organization (WHO) has stated that currently approved COVID vaccines are expected to remain effective against the XFG variant. The updated 2025-2026 COVID shots, which target LP.8.1, have been approved by the US Food and Drug Administration (FDA), but with restrictions limiting who is eligible to get the shot. The FDA's decision has fuelled concerns that the shots may only be available to the most at-risk Americans.
| Characteristics | Values |
|---|---|
| Name of the new strain | XFG COVID-19 variant, "Stratus" |
| Symptoms | Terrible headaches, fatigue, sore throats |
| Vaccine effectiveness | Expected to remain effective against the XFG variant |
| Vaccine eligibility | People over the age of 65 and those with a high-risk condition |
| Vaccine availability | New rules requiring clinical trials may delay access |
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What You'll Learn
Effectiveness of current vaccines against new strains
The SARS-CoV-2 virus is known to mutate often, leading to new strains that are more transmissible and better at evading immunity. As of September 2025, the XFG variant, also known as "Stratus", is the dominant strain in the US, causing a surge in COVID-19 cases. This strain was first detected in January 2025 in Southeast Asia and has since spread rapidly worldwide.
The World Health Organization (WHO) has stated that the currently approved COVID-19 vaccines are expected to remain effective against the XFG variant. Dr. William Schaffner supports this claim, stating that since the dominant strains are part of the Omicron family, the previous year's vaccine and the anticipated updated vaccines should cover these new strains. The updated 2025-2026 COVID shots, targeting the LP.8.1 strain, have been approved by the US Food and Drug Administration (FDA), but with restrictions limiting their eligibility to individuals over 65 and those at high risk for severe COVID-19.
The FDA's decision to recommend updating COVID-19 vaccines to target the LP.8.1 strain has sparked concerns about limited access to the shots. The LP.8.1 strain is a descendant of JN.1 and is closely related to the XFG variant. Studies by Moderna and Pfizer showed that a vaccine targeted at LP.8.1 induced a stronger immune response compared to the current COVID shots. However, the clinical trial requirement for updated COVID vaccines may delay access for those who want it, and it is unclear how many people will be needed for these trials.
To address the challenge of selecting the right strain for flu vaccines, MIT researchers have developed an AI tool called VaxSeer. This tool uses deep learning models trained on viral sequences and lab test results to predict dominant flu strains and identify the most protective vaccine candidates months in advance. VaxSeer has demonstrated strong correlations with real-world vaccine effectiveness estimates, improving the accuracy of vaccine selection and reducing reliance on guesswork.
In summary, while new COVID-19 strains like XFG continue to emerge, the currently approved vaccines are expected to remain effective, particularly the updated 2025-2026 shots. The ongoing development and approval of vaccines targeting specific strains, such as LP.8.1, aim to further enhance protection against the dominant variants. Additionally, the creation of tools like VaxSeer for flu vaccine strain selection can help improve the effectiveness of flu vaccines by making more accurate predictions about dominant strains.
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New strains and their transmissibility
The SARS-CoV-2 virus has mutated often since the start of the COVID-19 pandemic, resulting in new strains that are often more transmissible and better at evading immunity than their predecessors. For instance, the BA.2.12.1 variant, an offshoot of the Omicron BA.2, was found to be more transmissible than the variants before it. The B.1.1.7 variant, also known as the Alpha variant, was also more transmissible than the original strain of the COVID virus and caused a surge of infections worldwide.
The XFG variant, also known as the "Stratus" variant, is a recent example of a highly infectious new strain. It was first detected in Southeast Asia in January 2025 and spread rapidly worldwide, becoming the dominant variant in the US by September 2025. The Stratus variant is a recombinant or hybrid of two existing Omicron strains, LF.7 and LP.8.1.2, which may enhance its ability to bind to cells in the body and cause infection.
Vaccine makers have been updating COVID-19 vaccines to address new strains. The FDA selected the LP.8.1 strain for the fall 2025 COVID vaccines, citing its dominance in the US and its relationship to the previous dominant strain, NB.1.8.1 or "Nimbus". Moderna and Pfizer's studies showed that an LP.8.1-targeted vaccine induced a stronger immune response than the current COVID shots. However, the updated vaccine will likely only be available to high-risk individuals due to the FDA's clinical trial requirements.
Strain surveillance is crucial for pandemic response and ending the pandemic. Rapid and constant NGS sequencing of positive samples allows for early identification of mutants that pose a threat to human health, enabling the implementation of effective policies to limit the spread of emerging strains. Mathematical models, such as the coSIR model, have been developed to simulate the dynamics of COVID-19 and predict the impact of various control measures on virus transmission. These models indicate that transmission control policies, such as mask-wearing and social distancing, are highly effective in reducing mortality rates, especially for highly infectious strains.
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Vaccine eligibility and accessibility
The eligibility criteria for the COVID-19 vaccine have evolved over time, with the CDC and FDA updating their recommendations. As of 2025, the FDA has approved updated COVID-19 shots with certain restrictions in place. The current eligibility criteria give access to the vaccine to:
- All U.S. adults aged 65 and older, who are still eligible for vaccination.
- Younger adults and children with at least one chronic health condition, such as obesity or asthma, are considered high-risk individuals and are eligible.
- Children under 5 are no longer eligible for Pfizer's COVID-19 vaccine but can receive shots from Moderna and Novavax.
- Pregnant women and healthy children are no longer recommended to receive the COVID-19 vaccine by the CDC.
- Individuals with cardiovascular disease, including heart disease, are eligible for the new shots, as per the American College of Cardiology.
- People with certain underlying medical conditions that put them at higher risk of severe COVID-19 infection are also eligible, as advised by a healthcare provider.
The FDA's decision to update the COVID-19 vaccine strain to LP.8.1 has raised concerns about limited access to the shots, with the clinical trial requirement potentially causing delays. However, vaccine eligibility and accessibility vary based on local regulations and healthcare providers' recommendations. It is always advisable to consult with a healthcare professional to determine individual eligibility and the availability of vaccines.
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Symptoms of the new strain
The XFG Stratus strain of COVID-19 is a recombinant of two Omicron lineages and carries a set of spike protein mutations. It was designated a "variant under monitoring" by the World Health Organization (WHO) in June 2025. As of August 2025, the Stratus strain dominates in parts of San Francisco, Sacramento, and San Jose, making up more than half of all variants detected in these areas.
The Stratus strain exhibits a wider range of symptoms than previous variants, including congestion, gastrointestinal issues, and hoarseness or a dry, irritated throat. However, most cases remain mild, and the risk of severe illness is low, especially for those who are vaccinated or have previously been infected. The WHO has stated that the current approved COVID-19 vaccines are expected to remain effective against symptomatic and severe disease caused by the Stratus variant.
The symptoms of the Stratus strain may become noticeable anywhere from 2 to 14 days after becoming infected and can last up to two weeks. While the Stratus strain is more transmissible than previous variants, it does not appear to cause more severe illness or deaths. The rate of hospitalization and deaths has remained low, and there has been no increase in hospitalizations attributed to this strain as of July 2025.
It is important to note that standard COVID testing does not identify specific strains, so individuals are unlikely to know which variant they have contracted. However, simple measures such as vaccinations, wearing masks, and washing hands can help protect against infection and severe disease.
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The impact of new strains on hospitalizations
The SARS-CoV-2 virus, which causes COVID-19, frequently mutates, resulting in new strains that are often more contagious and better at evading the immune system than previous versions. The XFG variant, also known as "Stratus," is a recent example of a highly infectious new strain that has driven a surge in COVID-19 cases in the United States and worldwide.
The symptoms associated with the Stratus variant include hoarseness, sore throat, headaches, fatigue, and a scratchy throat, which can be similar to allergy symptoms. These symptoms may not be as severe as those seen with previous strains, and the World Health Organization (WHO) has assessed the public health risk posed by Stratus to be "low." However, even mild cases of COVID-19 can lead to significant complications, including long COVID symptoms, lung and pulmonary issues, and an increased risk of severe illness for individuals with compromised immune systems and pre-existing conditions.
Vaccination remains crucial in protecting against severe illness and reducing hospitalizations. The current COVID-19 vaccines are expected to remain effective against the Stratus variant, according to the WHO. Vaccine manufacturers are continuously updating their formulations to target circulating variants, and staying up-to-date with vaccinations offers the best protection, especially for high-risk individuals.
In addition to vaccination, public health measures such as masking in crowded indoor spaces and maintaining good health habits can help reduce the impact of new strains on hospitalizations by slowing their spread and reducing the overall disease burden.
Vaccine Availability Across the United States
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Frequently asked questions
The new strain, XFG or "Stratus", is expected to respond to the updated 2025-2026 COVID-19 vaccines, per the World Health Organization.
The FDA has restricted the updated vaccine to people aged 65 and older and younger individuals with underlying conditions that put them at high risk for severe COVID-19 infection.
The updated vaccine will be available at doctors' offices and pharmacies.
People aged 65 and older do not need a prescription. People aged 64 and younger do not need a prescription if they are getting the vaccine at a clinic. People aged 64 and younger may need a prescription if they are getting the vaccine at a retail pharmacy.
The updated vaccine will be available in the fall and winter seasons.
