A summer wave of COVID-19 continues to sweep the United States driven in large part by the highly contagious "FLiRT" COVID variants, including KP.3.1.1 and KP.3.
Following the news of multiple Olympic athletes testing positive for COVID-19 at the Paris Olympics and reports of surging wastewater levels in most states, it's clear that the virus is spreading rapidly in the U.S.— and it isn't showing any signs of slowing down.
Test positivity rates and COVID-related emergency room visits have been rising steadily across the U.S., especially in the West and South. Nationally, wastewater viral activity for COVID-19 has reached “very high” levels in recent weeks.
What's more, COVID-19 cases are either growing or likely growing in 32 states, according to the latest data from the U.S. Centers for Disease Control and Prevention.
According to some experts, the U.S. may be experiencing its biggest summer COVID wave yet, NBC News previously reported.
The surge is being driven by the new FLiRT strains — including KP.3, KP.2, and KP.1.1 — a family of fast-growing omicron subvariants that have been circulating in the U.S. since the spring.
Scientists nicknamed these variants “FLiRT” after the locations of their spike protein mutations, which may make them better at evading immunity than previous strains, experts say.
More recently, a descendant of KP.3 called KP.3.1.1 has gained steam and surpassed other variants to become the dominant strain. Currently, KP.3.1.1 makes up about 28% of cases with KP.3 trailing close behind, per the latest CDC data.
Together, the FLiRT variants account for around 75% of new cases nationwide.
How bad is this summer's COVID-19 wave? What are the symptoms of the FLiRT variants? Are vaccines effective? Here's what to know.
Is there a COVID-19 summer wave?
The U.S. is currently facing a sharp rise in COVID-19 infections, which many experts consider to be an anticipated summer wave, TODAY.com reported.
While the CDC no longer tracks the total number of cases in the U.S., there are clear indicators that COVID-19 is spiking across the country.
The most recent CDC data available show test positivity is at 17.6%, up from about 16% from the previous week. During last winter's COVID surge, test positivity peaked at around 12%, for comparison.
Wastewater data published by the CDC show that COVID-19 viral activity level is "very high" nationwide — it was considered "high" or "very high" for most of January and February. Levels are also "very high" in 27 states, as of Aug.9.
Hospitalizations and deaths, indicators of the severity of a COVID-19 wave, are rising as well but are still much lower compared to COVID-19 waves earlier in the pandemic.
The current COVID-19 trends are not entirely surprising to experts, as the country has seen waves in previous summers. Travel peaks in the summer months, and given the ongoing heat wave across the country, many are turning to indoor, air-conditioned gatherings, where the virus is more likely to spread.
The FLiRT variants and another new strain, LB.1 — a spinoff of JN.1 — are likely contributing to the surge in cases, along with waning population immunity, experts say. Due to their mutations, the FLiRT variants may also be better at evading the immune system.
Anecdotally, some people have reported becoming infected this summer for the first time after avoiding COVID-19 for the last four years, NBC News reported.
The seasonality of COVID-19 is something scientists are still trying to understand, but one thing remains clear: “This virus is now integrating itself into our population and our way of life,” Dr. William Schaffner, professor of infectious diseases at Vanderbilt University Medical Center, tells TODAY.com.
“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," Dr. Albert Ko, infectious disease physician and professor of public health, epidemiology and medicine at Yale School of Public Health, previously told TODAY.com.
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," Ko told TODAY.com in May.
In recent weeks, additional FLiRT subvariants have emerged and are gaining traction in the U.S. These include KP.3.1.1, a and KP.2.3, a direct descendent from KP.2.
The FLiRT variants have additional mutations that set them apart from JN.1 and appear to give them an advantage over previous variants, Ko added. 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 are 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,” Schaffner told TODAY.com in May.
In April, KP.2 quickly overtook JN.1, the omicron subvariant that drove a surge in COVID cases this past winter. In a matter of weeks, KP.3 surpassed KP.2 to become the most prevalent strain.
The proportion of cases caused by the FLiRT variants is still increasing, while the proportion caused by other strains is decreasing, which suggests the FLiRT variants have immune-escape features that give them an advantage over previous variants, 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.
What are the symptoms of KP.3?
“The FLiRT variants are probably not going to create very distinctive symptoms. It looks at the moment to follow the other subvariants,” Schaffner said.
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.
However, some people can develop severe COVID-19 symptoms requiring hospitalization. People over 65 years old, people with underlying health conditions, and people who are immunocompromised are at greatest risk.
Do vaccines protect against KP.3?
Early laboratory studies indicate that the current 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 initially voted to recommend a monovalent vaccine targeting the JN.1 variant for this fall. However, based on new data, the FDA now advises drugmakers to update vaccines to target the KP.2 strain, the agency said.
"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 by the 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.
