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A new, fast-spreading COVID-19 variant called KP.2 is circulating in the United States and driving an increasing proportion of cases, sparking concerns about a potential summer wave. KP.2 is part of a new family of variants, which scientists have nicknamed "FLiRT" after their mutations. Last month, KP.2 quickly overtook JN.1, the omicron subvariant that drove a surge in COVID cases this past winter, to become the dominant strain in the U.S. Currently, KP.2 accounts for over a quarter of infections nationwide, according to the latest data from the U.S. Centers for Disease Control and Prevention. During a two-week period ending on May 11, KP.2 made up an estimated 28.2% of cases in the U.S., up from about 6% in mid-April and just 1% in mid-March. After KP.2, the next most common variant is JN,1, which accounts for about 15% of cases, followed by two JN.1 subvariants, JN.1.7 and JN.1.16. Another FLiRT variant, called KP.1.1, is also circulating in the U.S., but is less widespread than KP.2. It currently accounts for about 7% of infections nationwide, per the CDC. Although cases and hospitalizations are down and the country appears to be in the middle of a COVID-19 lull, the new FLiRT variants are stoking fears about a wave of infections this summer. Scientists are warning that KP.2 and KP.1.1 may be better at evading the immune system due to their spike protein mutations, and that waning immunity and poor uptake of the latest COVID-19 vaccine have created a more susceptible population. Will there be another COVID-19 surge? What are the symptoms of the FLiRT variants? Are vaccines still effective? We spoke to experts to learn more. The FLiRT variants — KP.2 and KP.1.1 — are spinoffs of JN.1.11.1, a direct descendant of JN.1, and were initially detected in wastewater samples from across the country. The 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, 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 for their mutations, according to the Infectious Disease Society of America. Just like other COVID-19 strains that have gained dominance in the U.S. over the last year — JN.1, HV.1, EG.5 aka Eris, and XBB.1.16 or Arcturus — the FLiRT variants part of the omicron family. The emergence of KP.2 and other FLiRT variants is the "same old story," Andrew Pekosz, Ph.D., virologist at Johns Hopkins University, tells TODAY.com. The SARS-CoV-2 virus mutates and gives rise to a new, highly contagious variant, which becomes the dominant strain. "The timeline that it happens in, three to six months, is much faster than we see with other viruses like influenza," says Pekosz. "It's still early days, but the initial impression is that this variant (KP.2) is rather transmissible," Dr. William Schaffner, professor of infectious diseases at Vanderbilt University Medical Center, tells TODAY.com. The proportion of cases caused by KP.2 is increasing while the proportion caused by other variants is decreasing, which suggests KP.2 has features that give it an advantage, the experts note. KP.2 looks very similar to its parental strain JN.1, says Pekosz, which is highly contagious. "Except it has these two mutations. ... I think these two mutations together are making KP.2 a better virus in that it maintains its ability to transmit, but also now evades some of the pre-existing immunity in the population," says Pekosz. Over 97% of people in the U.S. have natural or vaccine-induced antibodies against the the SARS-CoV-2 virus, per the CDC, but this immune protection fades over time. Low vaccination rates and waning immunity create a vulnerable population, which may allow the FLiRT variants to take hold. Only time and more data will tell, the experts note. Laboratory studies suggest that KP.2 is mutated enough such that current vaccines and immunity from prior infection will only provide partial protection, says Schaffner. "We'll have to see how true that is, but it appears, over time to be becoming a more prominent variant," he adds. "It's still really early in the emergence of KP.2, but I don't think we need to sound the alarm bells as of yet," says Ko. It's too soon to tell whether the FLiRT variants will cause a summer wave or surge, the experts note. However, it is clear that COVID-19 is still circulating and won't be taking any time off. "We're seeing these infections year-round, at modulating levels. ... We're probably not at the stage yet where we'll see COVID go away completely at any time of the year," says Pekosz. Test positivity, which is an early indicator of case levels, is at 3% as of April 20, down 0.4% from the previous week and a sharp decline from around 12% in mid-January, per the CDC. (The CDC no longer tracks the total number of cases in the U.S.) "We're not seeing a lot of hospitalizations, and we're certainly much lower than we were in the winter, so I'd say right now we're at a low point, which is reassuring," says Ko. Wastewater data published by the CDC show that the viral activity level for COVID-19 is currently "minimal" — 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 usually the big peaks are in the winter, when people are inside and in more contact," says Ko. COVID-19 has caused summer waves in the past, the experts note, which are often smaller than the winter surges. "I don't think that we'll see any kind of massive surge in cases," says Pekosz. Speculating based on current COVID-19 trends, Ko says, "KP.2 may cause a small wave, but not necessarily the large peaks that we saw in the winter — again, it is too early to tell." The seasonality of COVID-19 is something scientists are still trying to understand. But one thing is obvious: "This virus is now integrating itself into our population and our way of life," says Schaffner. There are several reassuring factors, says Ko. First, KP.2 is not a highly divergent variant — in other words, it doesn't have a very large number of new mutations that differentiate it from other strains. Second, many people have immunity from recently being infected with the FLiRT variant predecessor JN.1. Last, during the summertime, people are spending less time indoors, which allows the virus fewer opportunities to spread. "I'm not expecting a large surge in the summer, but again, we have to be cautious and we have to follow the data," says Ko. "We always have to be humble because SARS-CoV-2 has taught us a lot of new things." It is still too early to tell whether the symptoms of KP.2 and other FLiRT variants are different from previous strains. "The FLiRT variants are probably not going to create very distinctive symptoms. It looks at the moment to follow the other subvariants," says Schaffner. The symptoms of the FLiRT variants are similar to those caused by JN.1, which include: 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 usually depend more on a person's underlying health and immunity rather than the variant that caused the infection. Similar to JN.1 and other omicron subvariants, the FLiRT variants seem to be causing milder infections, says Schaffer. "There's no evidence now that makes us think KP.2 is more virulent or more able to cause severe disease than the prior variants," says Ko. "Early laboratory studies indicate that the vaccines will continue to provide protection against KP.2 — a little less protection, but not zero by any means," says Schaffner. As the virus mutates, it is becoming progressively different from the omicron strain targeted in the latest updated booster released in the fall of 2023. "We would expect that to happen, and we anticipate the plan is to have an updated vaccine in the fall available to everyone," says Schaffner. Preliminary laboratory data from Japan, which has not been peer-reviewed, suggests that the current COVID-19 vaccines in the U.S. may be less effective against KP.2 than against JN.1, NBC News previously reported. The Food and Drug Administration has delayed a May 16 meeting to decide which strains to include in an updated vaccine for the fall. "The additional time will allow the agency to obtain more up-to-date surveillance data and other information on the circulating strains of SARS-CoV-2 to better inform the committee's discussions and recommendations," an FDA spokesperson told NBC News. Even if vaccines do not prevent infection, they can still offer some protection by preventing severe disease, hospitalization, and COVID-19 complications, TODAY.com previously reported. "It's still clear that the more severe cases that come into the emergency room predominate in people who either are not up to date on their vaccines or haven't gotten a vaccine in a really long period of time," says Pekosz. Vaccination is especially important for the elderly, says Pekosz, which is why the CDC recently recommended adults ages 65 and older get an additional dose of the 2023-2024 updated COVID-19 vaccine. Unfortunately, vaccination uptake is still poor, the experts note. "The vaccines are still showing signatures of effectiveness, but they're not being utilized anywhere close to the level that they should be," says Pekosz. As of April 27, 2024, only about 22% of adults and 14% of children have reported receiving the updated COVID-19 vaccine released in September 2023, according to the CDC. All current PCR and at-home tests are recognizing KP.2 and other FLiRT variants, the experts note. (Though if you have symptoms of COVID and test negative, it's a good idea to stay home to avoid potentially exposing other people, TODAY.com previously reported. If you are using an at-home antigen test, always remember to check the expiration date and whether it's been extended by the U.S. Food and Drug Administration. "Antivirals (such as Paxlovid) are also working well. ... There's not any major signals of antiviral resistance in the population, which is a positive sign," says Pekosz. While it's too early to tell how the FLiRT variants will pan out this summer, people can always take steps to protect themselves and others against 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 an exposure. Stay home when you are sick. Return to normal activities only after you have been fever-free and symptoms have been improving for at least 24 hours. Practice good hand hygiene. Improve ventilation. Wear a mask in crowded, indoor spaces. Practice social distancing. This article was originally published on TODAY.comWhat are the FLIRT variants?
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