FLiRT Overview: What It Is, Symptoms, and Prevention

What is FLiRT? What exactly is this subvariant called FLiRT, why is it considered a type of FLiRT in Russia, how dangerous is FLiRT, what are the symptoms of a FLiRT infection, what complications can arise, who is at risk, how is FLiRT treated and prevented, and could there be a new disease wave?

What is FLiRT?

FLiRT is a subvariant of the Omicron lineage that helped drive last winter’s COVID-19 surge and now forms several smaller branches such as KP.2, KP.3, KS.1, and LB.1. It was first detected in November 2023 in India. After that, the strain appeared in other countries, including the United States, the United Kingdom, South Korea, and Russia. This pattern of spread reflects how rapidly variants can travel through travel, communities, and close contacts.

Why is FLiRT called that?

The name FLiRT comes from the spike protein mutations that carry the letters F, L, R, and T. The spike protein helps the virus bind to and enter host cells, and changes in these regions can help the virus dodge parts of the immune response and infect people who were previously ill or vaccinated. At the same time, changes in the spike configuration can sometimes reduce binding efficiency, so the exact effects of this strain require ongoing study.

FLiRT Strain in Russia

In Russia, health authorities reported 178 FLiRT-related cases through May 2024. In September 2024, there was a sharp uptick in the share of this variant among circulating strains, with estimates suggesting the proportion rose about 2.5 times in the first half of September. This rise, combined with typical seasonal factors, contributed to a noticeable increase in confirmed COVID-19 cases in late summer and early autumn 2024. Health officials stressed that continued surveillance and adherence to preventive measures remain important as the situation evolves.

How dangerous is FLiRT?

FLiRT carries spike-protein mutations that can help the virus elude parts of the immune response while keeping the ability to infect cells. The LB.1 and KP.3 variants are noted as more transmissible than earlier strains, and the LB.1 mutation may further reduce immune recognition. While some experts caution that vaccination effectiveness may be somewhat reduced for certain individuals, they also emphasize that vaccines continue to provide strong protection against severe disease and hospitalization. In assessments from public health and academic centers, the balance between immune evasion and binding to cell receptors is described as the virus’s ongoing tuning process as it evolves.

Independent virologists highlight that the virus’s evolution is linked to how the immune system recognizes it and how readily it can attach to targets on human cells. The overall picture is nuanced: higher spread does not automatically mean higher mortality, and outcomes depend on age and underlying health. A virology expert affiliated with a major research institution noted that the high contagiousness largely results from immune recognition gaps, while individual responses vary widely. (citation: Johns Hopkins Institute)

Symptoms of FLiRT infection

The set of symptoms reported for FLiRT infection matches what is seen with other SARS-CoV-2 variants: fever or chills, cough, shortness of breath or breathing difficulty, sore throat, nasal congestion or runny nose, loss of taste or smell, fatigue, body aches, headaches, nausea, and diarrhea. As with other variants, the timing from exposure to symptoms remains around five days, and individuals can be contagious about two days before symptoms begin. Symptom severity depends more on a person’s overall health and immune status than on the variant itself. (citation: Yale Medicine)

Experts caution that there is still limited definitive data on whether new subvariants cause more severe disease. The course of illness varies from person to person, and the key driver of outcomes remains the immune system and general health rather than the specific variant alone. Doctors emphasize the importance of timely testing, especially when exposure is suspected. (citation: Johns Hopkins Institute)

What complications can FLiRT cause?

Like other coronavirus subvariants, FLiRT can lead to serious complications such as the formation of blood clots, myocarditis, pneumonia, and acute respiratory distress syndrome. Some survivors experience post-COVID syndrome, with lingering fatigue, shortness of breath, mood changes, and cognitive difficulties that may persist for months. Studies from major research centers indicate a substantial portion of recovered individuals report neurological or other long-term symptoms. The exact frequency varies by population and health status.

Health researchers stress that disease progression is influenced by the person’s health and immune background, and ongoing monitoring is essential as the virus continues to evolve.

Vadim Rassokhin, a leading researcher at the Pasteur Institute’s immunology and virology program, notes that up to a significant share of people who have had COVID-19 report long-term effects, underscoring the importance of recognizing and addressing these symptoms as part of public health planning.

Who is at risk of infection

According to the latest assessments, four groups are at higher risk of FLiRT infection.

1. People with weakened immune systems, including those undergoing chemotherapy, organ transplant recipients, or individuals on immunosuppressive medications. Their bodies may not respond as robustly to infections, making severe disease more likely.
2. Older adults, as immune response tends to decline with age.
3. Service workers who have direct contact with patients and the public, such as doctors, nurses, cleaners, teachers, public transport staff, and food service workers.
4. People with chronic conditions such as cardiovascular disease, diabetes, lung disease, or obesity, which can worsen outcomes.

Treating and preventing infection with FLiRT

Prevention and treatment mirror those for other COVID-19 types. Health professionals advise simple steps: cover your mouth and nose when sneezing or coughing, stay current with vaccines and boosters, and stay home if unwell. Regular hand washing, good ventilation, and disinfecting surfaces are recommended, and extra precautions are advised for older adults, individuals with weakened immune systems, and children. Public health authorities emphasize the importance of timely testing and medical consultation if symptoms appear. (citation: Rospotrebnadzor)

Vaccination remains a critical tool, along with mask use in crowded settings and avoiding close contact with sick individuals. Those at higher risk should take additional precautions and seek medical advice promptly if symptoms develop.

Will there be an outbreak?

Many health experts warn that FLiRT can spread efficiently, creating a risk of a renewed COVID-19 wave. Mutations in viruses are often unpredictable and can accelerate transmission, prompting questions about the need for targeted prevention or a new vaccine for this subvariant. The ultimate likelihood of a large outbreak depends on public adherence to precautions and vaccination coverage, along with ongoing surveillance by health authorities. (citation: expert interview)