FLiRT and LB.1: Understanding the Latest COVID Variants and Their Symptoms
Unexpected symptom shifts and booster updates are key to navigating this latest wave.
FLiRT and LB.1: The Latest COVID Variants You Need to Know About
As we move further into 2025, a fresh rise in COVID-19 cases is being fueled by the emergence of new variants, particularly the FLiRT variants (including KP.3.1.1, KP.3) and the LB.1 variant. Although these variants are not causing as severe illness as earlier strains, their rapid spread and evolving symptoms have prompted renewed attention from health experts and the public alike. Understanding the current landscape of COVID variants, symptoms, and preventive measures is crucial for navigating this unprecedented summer surge.
Current Landscape: What Are FLiRT and LB.1 Variants?
The term FLiRT refers to a group of related COVID-19 variants based on their spike protein mutations, named after the key mutations—F, L, R, and T. These arise from the Omicron JN.1 lineage, the same family that dominated previous COVID waves. The most notable FLiRT variants are now driving the majority of U.S. infections, with KP.3.1.1 accounting for approximately 27.8% and KP.3 for 20.1% of new cases as of early August 2025. Meanwhile, the LB.1 variant—which is genetically distinct from the FLiRT line—accounts for around 16% of current infections, making it another key player to monitor in the ongoing pandemic landscape.
- FLiRT variants: Descendants of Omicron JN.1, including KP.3, KP.2, KP.3.1.1, and other close relatives.
- LB.1 variant: A separate lineage rising in the U.S., not classified under the FLiRT umbrella.
Both types of variants are highly transmissible. According to infectious disease specialists, neither seems to be notably more dangerous in terms of severe illness, but they are contagious enough to warrant concern, especially among high-risk groups.
Is There a Summer COVID Surge?
Yes, current data shows a significant uptick in COVID-19 activity during the summer months, as tracked by the CDC’s wastewater surveillance program. In early August, viral activity levels were listed as “very high,” with cases rising nationally. This pattern is not unique to FLiRT or LB.1—in fact, summer surges have occurred in several past pandemic years.
Factors contributing to the summer surge:
- Increased travel during summer break brings people into contact with more communities and potential infection sources.
- Indoor gatherings, especially as people escape the heat in air-conditioned settings, increase close-contact transmission opportunities.
- Waning immunity, with fewer adults and children having received updated boosters, has reduced community-level protection.
How Contagious Are the New Variants?
The latest COVID-19 FLiRT and LB.1 variants are highly contagious. Their spike mutations allow them to evade some pre-existing immunity (from prior infection or vaccination) more readily than older variants. As a result, these variants spread quickly in communities, even among people who consider themselves protected.
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Despite this, available evidence suggests that while transmissibility has increased, these variants have not led to a commensurate rise in hospitalizations or deaths. The reason for this appears to be growing baseline immunity from years of infections and vaccinations, even if that immunity is imperfect or waning. However, vulnerable individuals—such as the elderly, immunocompromised, or those with chronic health conditions—remain at higher risk of complications and should take extra precautions.
Are the Symptoms Different with FLiRT and LB.1?
Experts report that the symptom profile of FLiRT and LB.1 closely resembles previous Omicron variants, but some subtle shifts have been observed. The symptoms can vary from mild to severe, with most cases presenting as mild upper respiratory infections.
- Fever or chills
- Cough
- Runny or stuffy nose
- Sore throat
- Fatigue and muscle aches
- Headache
- Body aches
- Shortness of breath or difficulty breathing
- Loss of taste or smell (still possible, but less common than early in pandemic)
- Gastrointestinal symptoms (nausea, diarrhea, abdominal discomfort — occasional)
Persistent cough, sore throat, and elevated fever are especially notable. According to physicians, anyone experiencing these symptoms should consider getting tested for COVID-19, particularly if they have exposure or live in a region reporting high transmission rates.
Who Is Most at Risk from FLiRT and LB.1?
While most people experience mild to moderate illness, certain individuals are at higher risk for severe outcomes. These include:
- Seniors age 65 and older
- People with underlying medical conditions, such as diabetes, heart disease, lung disease, or weakened immune systems
- Pregnant individuals
- Unvaccinated or incompletely vaccinated individuals
Even among lower-risk populations, complications are possible. Therefore, heightened awareness and timely action are recommended, particularly as summer social calendars ramp up.
Are the Current Tests and Treatments Effective?
Currently available at-home rapid tests and PCR tests can still reliably identify infections with FLiRT and LB.1 variants. These tests remain a valuable tool for interrupting chains of transmission and making informed decisions about self-isolation and medical care.
Treatment:
- Antiviral medications, such as Paxlovid, remain effective against these new variants and are especially recommended for high-risk individuals.
- Supportive care includes rest, hydration, fever reducers (like acetaminophen), and symptom management as needed.
Severe cases should be referred to healthcare professionals for evaluation and treatment plans, particularly if symptoms worsen or persist beyond a few days.
Vaccination: What’s the Latest Guidance?
Vaccination continues to be the most crucial public health tool for reducing severe illness, hospitalizations, and deaths from COVID-19. Uptake of the latest boosters, however, has lagged. As of May 2024, only about 22.5% of American adults were up to date on the most recent COVID-19 vaccine.
The U.S. Food and Drug Administration (FDA) and CDC update their vaccine recommendations regularly to address the circulating strains. The upcoming vaccine formula, expected by September 2025, has been updated to target the new subvariants—including those in the FLiRT lineage.
- People aged 6 months and older are recommended to receive the updated vaccine as soon as available.
- Vaccination is especially important for elderly, children, and those with chronic conditions.
Prevention: How Can You Protect Yourself and Others?
With the current wave showing a steep trajectory, experts emphasize adhering to established prevention strategies—particularly in high-risk environments or during local surges.
- Stay home when sick: Follow the latest CDC guidelines, remaining isolated until symptoms improve and you are fever-free for at least 24 hours without the use of fever-reducing medications.
- Mask up: Especially in crowded or poorly ventilated indoor spaces, and for at least five days after resuming normal activities post-infection.
- Hand hygiene: Wash hands frequently with soap and water or use hand sanitizer when unable to wash.
- Test for COVID-19: At the first sign of symptoms or after suspected exposure, test and follow medical advice.
- Ventilation: Spend time in well-ventilated areas, or open windows when possible during indoor gatherings.
- Stay up to date on vaccines: Receive COVID-19 boosters as recommended to ensure the best available protection.
These measures are effective at breaking transmission chains and lessening the community burden of disease.
Why Are Variants Still Emerging?
The COVID-19 virus continues to mutate as it spreads, producing a cascade of new variants. Some mutations allow the virus to move through populations more efficiently or sidestep partial immune defenses. This rapid evolution presents challenges for vaccine formulation, public health forecasting, and day-to-day decision-making.
Vaccine regulators must continually assess global sequence data to determine which strains to include in upcoming shots. The FDA, for instance, moved swiftly in mid-2025 to advise manufacturers to update the fall booster to better match the prevailing FLiRT strains after observing their dominance over earlier subvariants.
How to Tell COVID-19 FLiRT or LB.1 From Allergies, Colds, or the Flu?
The symptoms of FLiRT and LB.1 can be similar to those of allergies, common colds, or influenza, making it challenging to distinguish without testing. Typical COVID-19 features—such as loss of taste or smell—have become less common, driving greater overlap with other respiratory illnesses.
| Symptom | COVID FLiRT/LB.1 | Flu | Allergy | Common Cold |
|---|---|---|---|---|
| Fever | Often | Often | Rare | Rare |
| Sore Throat | Common | Can occur | Occasional | Common |
| Cough | Common | Common | Sometimes | Common |
| Loss of Taste/Smell | Occasional | Rare | No | Rare |
| Runny Nose | Common | Sometimes | Very common | Common |
| Fatigue | Common | Common | Sometimes | Sometimes |
| Body Aches | Common | Common | Rare | Sometimes |
| Itchy Eyes | Rare | Sometimes | Very common | Rare |
| GI Symptoms | Occasional | Occasional | Rare | Rare |
Testing remains the best way to confirm a COVID-19 infection, given the high degree of symptom overlap.
What To Do If You (or a Loved One) Test Positive
- Stay home: Isolate immediately to avoid transmitting the virus to others, particularly high-risk individuals.
- Start symptomatic care: Rest, hydrate, and manage fever or aches with approved medications.
- Monitor for worsening symptoms: Seek medical advice if breathing becomes difficult, you develop chest pain, or symptoms do not improve after a few days.
- Resume activities safely: After at least 24 hours fever-free and with improved symptoms, you may resume activities, but continue precautions (masking, distancing) for at least five days.
- Notify close contacts: So that others can test and take precautions as needed.
Frequently Asked Questions (FAQs)
Q: Are the FLiRT and LB.1 variants more dangerous than previous COVID variants?
A: Current evidence suggests that while FLiRT and LB.1 are more transmissible, they do not cause more severe illness than past Omicron variants. Hospitalization and death rates remain comparatively low, largely thanks to greater population immunity.
Q: Can children get infected with FLiRT or LB.1?
A: Yes, both children and adults can catch these new variants. Children generally experience mild illness, but severe outcomes are possible, especially for those with underlying conditions. Vaccination and good hygiene are recommended for all age groups.
Q: Will the current COVID vaccine protect against FLiRT and LB.1?
A: The updated vaccines expected in Fall 2025 are being formulated to better target the prevailing FLiRT strains. Even before the update, vaccination provides some protection against severe illness and hospitalization, though breakthrough infections can occur.
Q: Are masks still necessary?
A: Masks remain an effective tool, especially during local outbreaks, in crowded or poorly ventilated settings, and for those with increased risk. Expert guidance continues to recommend mask usage post-infection and in high-exposure environments.
Q: What’s the best way to minimize my risk of infection?
A: Stay up to date on vaccinations, practice hand hygiene, wear masks when appropriate, avoid large gatherings if feeling ill, and test when you have symptoms or after suspected exposure.
Key Takeaways
- FLiRT and LB.1 variants are currently driving a summer COVID-19 surge in the U.S., with high transmissibility but no evidence of increased severity compared to past Omicron strains.
- Symptoms remain varied but are generally similar to past COVID-19 waves. Timely testing and isolation remain critical.
- Vaccination, testing, and preventive behaviors are still our best defenses as the virus continues to evolve.
References
- https://www.southshorehealth.org/wellness/blog/four-things-you-should-know-about-covid-flirt
- https://www.medstarhealth.org/blog/flirt-covid
- https://www.goodhousekeeping.com/health/a61830829/covid-flirt-lb1-variant-symptoms/
- https://publichealth.jhu.edu/2024/what-to-know-about-covid-flirt-variants
- https://www.goodhousekeeping.com/health/a61972576/new-covid-19-booster-2024/
- https://www.youtube.com/watch?v=y5O4M5hKZCs
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