In recent weeks, a new variant of COVID-19 called KP.3 has gained dominance in the United States. KP.3 is part of a family of mutated strains dubbed “FLiRT,” which are causing a growing proportion of cases across the country. As KP.3 expands, some are concerned about a possible summer surge.
FLiRT strains — which include KP.3, KP.2 and KP.1.1 — now account for more than half of all COVID-19 infections nationwide, according to the latest data from the state Centers for Disease Control and Prevention -United.
These new variants, which scientists have dubbed “FLiRT” after the location of their spike protein mutations, have been circulating in the United States since early spring. In April, KP.2 quickly overtook JN.1, the omicron subvariant that led to a surge in COVID cases last winter.
Within weeks, the KP.3 variant overtook the KP.2 variant to become the most common strain in the United States, according to the CDC.
During a two-week period ending June 8, KP.3 accounted for about 25% of cases in the United States, up from about 9% in early May. After KP.3, the second most common variant is KP.2, another FLiRT variant that gained popularity in May and now accounts for approximately 22% of cases. It is followed by LB.1, a JN.1 sub-variant and another FLiRT variant, KP.1.1.
Together, the FLiRT variants account for approximately 55% of cases in the United States.
Although hospitalizations are down and the number of COVID-19 cases is relatively low, there has been a slight increase in positive tests and emergency room visits, according to the latest CDC data. These trends, along with previous summer waves, have fueled fears of a surge in infections this summer.
Scientists warn that FLiRT variants may be better at evading the immune system due to their spike protein mutations, and that waning immunity and low uptake of the latest COVID-19 vaccine have created a more susceptible population.
Will there be another wave of COVID-19? What are the symptoms of FLiRT variants? Are vaccines still effective? We spoke with experts to find out more.
What is KP.3?
KP.3 is one of the FLiRT variants – along with KP.2 and KP.1.1 – that are spinoffs of JN.1.11.1, a direct descendant of JN.1. They were initially detected in wastewater samples from across the country.
KP.3 and the other new variants have additional mutations that set them apart from JN.1 and appear to give them an advantage over previous variants, Dr. Albert Ko, an infectious disease physician and professor of public health, epidemiology and medicine at Yale School. of public health, tells TODAY.com.
The nickname “FLiRT” is based on the technical names of their mutations, according to the Infectious Disease Society of America.
Much like other strains of COVID-19 that have gained dominance in the United States over the past year – JN.1, HV.1, EG.5 aka Eris and XBB.1.16 or Arcturus – the FLiRT variants are part of the omicron family.
The emergence of KP.3 and other FLiRT variants is “the same old story,” Andrew Pekosz, Ph.D., a virologist at Johns Hopkins University, told TODAY.com. The SARS-CoV-2 virus mutates and gives rise to a new, highly contagious variant, which becomes the dominant strain. “The time frame in which this happens, in three to six months, is much faster than that seen with other viruses like the flu,” says Pekosz.
Is KP.3 more transmissible?
“It’s still early, but the first impression is that this variant is quite transmissible,” Dr. William Schaffner, professor of infectious diseases at Vanderbilt University Medical Center, told TODAY.com.
The proportion of cases caused by KP.3 is increasing, while the proportion caused by other variants is decreasing, suggesting that FLiRT variants possess characteristics that give them an advantage, experts note.
According to the CDC, more than 97% of Americans have natural or vaccine-induced antibodies to the SARS-CoV-2 virus, but this immune protection fades over time.
Low vaccination rates and waning immunity create a vulnerable population, which could allow FLiRT variants to take hold. Only time and more data will tell, experts note.
Laboratory studies suggest that FLiRT variants are mutated enough that current vaccines and immunity from prior infection provide only partial protection, Schaffner says. “We will have to see how true this is, but it seems that over time it is becoming a more prominent variant,” he adds.
“It’s still very early… but I don’t think we need to sound the alarm yet,” Ko says.
The State of COVID in the United States
It’s too early to tell whether the KP.3 and FLiRT variants will cause a summer wave or surge, experts note. However, it is clear that COVID-19 is still circulating and will not take a break.
“We’re seeing these infections throughout the year, at modulated levels. … We’re probably not at the stage yet where we’ll see COVID completely disappear at any time of the year,” Pekosz says.
Test positivity, which is an early indicator of case levels, was 5.4% as of June 8, up 0.8% from the previous week but down sharply from a peak of around 12% as of mid-January, according to the CDC. (CDC no longer tracks total U.S. cases)
“We’re not seeing a lot of hospitalizations, and we’re certainly a lot lower than in the winter, so I would say right now we’re at a low point, which is reassuring,” Ko says.
Wastewater data released by the CDC shows that the level of COVID-19 viral activity is currently “low” – it was considered high or very high for most of January and February.
“It seems like transmission is pretty low right now, and that makes sense because the biggest spikes usually occur in the winter, when people are indoors and in more contact,” Ko says.
In the past, COVID-19 has caused summer waves, experts note, which are often smaller than winter waves. “I don’t think we’ll see any massive increase in cases,” Pekosz says.
The seasonality of COVID-19 is something scientists are still trying to understand. But one thing is obvious: “This virus is now embedded in our population and our way of life,” Schaffner says.
Ko adds: “I don’t expect a big increase this summer, but again we have to be careful and follow the data. … We must always be humble, because SARS-CoV-2 has taught us many new things.”
What are the symptoms of KP.3?
It is still too early to tell if the symptoms of KP.3, KP.2 and other FLiRT variants are different from those of previous strains.
“FLiRT variants are unlikely to create very distinctive symptoms. At the moment it seems to follow the other sub-variants,” explains Schaffner.
Symptoms of FLiRT variants are similar to those caused by JN.1, including:
- Sore throat
- Cough
- Fatigue
- Congestion
- Runny nose
- Headache
- Muscle aches
- Fever or chills
- New loss of sense of taste or smell
- Shortness of breath or difficulty breathing
- Nausea or vomiting
- Diarrhea
According to the CDC, the type and severity of symptoms a person experiences generally depends more on their underlying health and immunity than on the variant causing the infection.
Similar to JN.1 and other omicron subvariants, FLiRT variants appear to cause milder infections, Schaffer says.
Do vaccines protect against KP.3?
Early lab studies indicate that vaccines will continue to offer protection against FLiRT variants – “a little less protection, but by no means zero,” says Schaffner.
As the virus mutates, it gradually becomes different from the omicron strain targeted in the latest updated booster released in fall 2023. “We expect this to happen, and we anticipate that an updated vaccine day will be available in the fall.” to everyone,” Schaffner says.
Advisors to the U.S. Food and Drug Administration met Tuesday (June 5) to decide which strains to include in updated COVID-19 vaccines for 2024-2025. The committee voted unanimously to recommend a monovalent vaccine targeting the JN.1 variant for this fall, the agency said in a press release.
Even though vaccines don’t prevent infection, they can still provide some protection by preventing severe illness, hospitalizations and complications from COVID-19, TODAY.com previously reported.
“It is still clear that the most serious cases that arrive in the emergency room mainly concern people who are not up to date with their vaccinations or who have not received a vaccine for a very long time,” says Pekosz.
Vaccination is especially important for older adults, Pekosz says, which is why the CDC recently recommended adults ages 65 and older receive an additional dose of the COVID-19 vaccine updated for 2023-2024.
Unfortunately, the vaccination rate is still low, experts note. “Vaccines still show signs of effectiveness, but they are not used at the level they should be,” says Pekosz.
As of April 2024, only about 22% of adults and 14% of children reported receiving the updated COVID-19 vaccine released in September 2023, according to the CDC.
All current PCR and at-home tests recognize KP.3 and other FLiRT variants, experts note. (However, if you have COVID symptoms and test negative, it’s a good idea to stay home to avoid potentially exposing others, TODAY.com previously reported.
If you use an at-home antigen test, remember to check the expiration date and whether it has been extended by the FDA.
“Antivirals (like Paxlovid) also work well. … There are no major signs of resistance to antivirals in the population, which is a positive sign,” says Pekosz.
How to protect yourself against the KP.3 and FLiRT variants
Although it is too early to tell how FLiRT variants will develop this summer, people can still take steps to protect themselves and others from COVID-19.
The CDC recommends the following prevention strategies:
- Stay up to date with COVID-19 vaccines.
- Test for COVID-19 if you have symptoms or exposure.
- Stay home when you are sick.
- Resume normal activities only after you no longer have a fever and symptoms have improved for at least 24 hours.
- Practice good hand hygiene.
- Improve ventilation.
- Wear a mask in crowded indoor spaces.
- Practice social distancing.
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