COVID-19 infections are rising across the country in large part due to the now-dominant KP.3 variant, prompting concerns about a summer COVID wave. KP.3 currently accounts for over 33% of new cases.
What's more, COVID cases are on the rise in 39 states, the U.S. Centers for Disease Control and Prevention reported in mid-June. A CDC map similarly shows cases do not seem to be declining anywhere in the country.
KP.3 is part of a family of highly contagious, mutated variants called the FLiRT variants — which include KP.3, KP.2 and KP.1.1. Combined, they are driving nearly two-thirds, about 62%, of COVID-19 infections nationwide.
These new variants, which scientists dubbed "FLiRT" after the locations of their spike protein mutations, have been circulating in the U.S. since the early spring.
Although COVID-19 numbers are still relatively low compared to the winter, CDC data shows an increase in test positivity and emergency room visits in recent weeks. The COVID-19 death and hospitalization rates are also on the rise.
Will there be another summer COVID-19 surge? What are the symptoms of the FLiRT variants? Are vaccines still effective? Here's what to know.
Is there a summer COVID surge?
The U.S. is currently in the midst of a summer COVID wave, NBC News reported, citing recent CDC data.
The data show that cases are on the rise in 39 states and not declining in any states. Hospitalizations, emergency room visits and deaths also appear to be on the rise.
The most recent CDC data available show test positivity up 6.6%. The CDC no longer tracks the total number of cases in the U.S.
“It looks like the summer wave is starting to begin,” Dr. Thomas Russo, chief of infectious diseases at the University at Buffalo Jacobs School of Medicine and Biomedical Sciences, told NBC News.
That said, wastewater datapublished by the CDC show that the viral activity level for COVID-19 is currently “low” — it was considered high or very high for most of January and February.
There have been COVID-19 waves in previous summers. People often travel in the summer, and given the ongoing heat wave, people may be turning to indoor, air-conditioned gatherings, where the virus is more likely to spread.
The new FLiRT variants and another one on the rise — LB.1, a JN.1 subvariant — may also be contributing to the recent uptick in cases, along with waning immunity and poor uptake of the latest COVID-19 vaccine, experts say.
Due to their mutations, the FLiRT variants may be better at evading the immune system. And apaperthat has yet to be peer-reviewed released earlier in June found that LB.1 may be even more infectious than the FLiRT variants.
The most recent CDC data available show KP.3 making up an estimated 33% of cases in the U.S., up from less than 10% in May. After KP.3, the next most common variant is KP.2, which accounts for about 21% of cases, followed by LB.1, and KP.1.1 which account for 17% and 9% of cases, respectively.
In April, KP.2 quickly overtookJN.1, the omicron subvariantthat drove asurge in COVID cases this past winter. In a matter of weeks, KP.3 surpassed KP.2 to become the most prevalent strain.
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.
Adds Ko: “I’m not expecting a large surge in the summer, but again, we have to be cautious and we have to follow the data. ... We always have to be humble because SARS-CoV-2 has taught us a lot of new things.”
What is KP.3?
KP.3 is one of the FLiRT variants — along with KP.2 and KP.1.1 — which 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 is a new omicron subvariant, which, along with its 'sister' variant KP.2, has emerged in the past month and is now causing the majority of COVID-19 infections," Dr. Albert Ko, infectious disease physician and professor of public health, epidemiology and medicine at Yale School of Public Health, tells TODAY.com.
KP.3 and the other FLiRT variants have additional mutations that set them apart from JN.1 and appear to give them an advantage over previous variants, says Ko.
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, andXBB.1.16 or Arcturus — the FLiRT variants part of the omicron family.
The emergence of KP.3 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.
Is KP.3 more transmissible?
“It’s still early days, but the initial impression is that this variant is rather transmissible,” Dr. William Schaffner, professor of infectious diseases at Vanderbilt University Medical Center, previously told TODAY.com.
The proportion of cases caused by KP.3 is increasing, while the proportion caused by other variants is decreasing, which suggests the FLiRT variants have features that give it an advantage, the experts note.
“The (FLiRT) mutations appear to make the KP.3 variant more transmissible than JN.1,” says Ko. “But I think the good news is that there’s no evidence showing that it’s more virulent or that it’s causing more hospitalizations or deaths.”
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 the FLiRT variants are 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 ... but I don’t think we need to sound the alarm bells as of yet,” says Ko.
What are the symptoms of KP.3?
It is still too early to tell whether the symptoms of KP.3, 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.
Do vaccines protect against KP.3?
Early laboratory studies indicate that the vaccines will continue to provide protection the FLiRT variants — "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.
Advisers to the U.S. Food and Drug Administration met in early June to decide which strains to include in the updated COVID-19 vaccines for 2024–2025. The committee unanimously voted to recommend a monovalent vaccine targeting the JN.1 variant for this fall, the agency said in a press release.
"It's with the assumption that future variants or future mutants will emerge from the (dominant) omicron subvariants we've experienced most recently," says Ko.
"But again, there's always a lot of uncertainty about where the next mutant is going to come from ... will it come from KP.3, KP.2 or from something upstream like JN.1?" Ko adds.
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 May 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.3 and other FLiRT variants, the experts note. (Although 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 bythe FDA.
“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.
How to protect against KP.3 and FLiRT variants
With COVID-19 cases on the rise again, consider taking steps to protect yourself and others against infection.
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.
Caroline Kee
Caroline Kee is a health reporter at TODAY based in New York City.
