Will FLiRT COVID variants bring another summer surge? What to know about symptoms and potential for spread

“This is not a surprise; this is always in the cards,” Edwin Michael, PhD, an epidemiologist at the University of South Florida College of Public Health, tells Fortune. “The mutations will keep happening.”

The Omicron variant of SARS-CoV-2, the coronavirus that causes COVID-19, has been circling the globe for nearly three years. In the U.S., the Centers for Disease Control and Prevention (CDC) classified it as a “variant of concern” in November 2021. The original Omicron strain, B.1.1.529, has since mutated into a number of subvariants, from BA.2.74 to XBB.1.16. Now a subvariant called KP.2 is the dominant strain nationwide, accounting for 29% of infections during the two-week period ending May 25, per the CDC’s COVID Data Tracker.

KP.2, KP.3, and KP.1.1 are among the Omicron subvariants in the FLiRT family, which isn’t a cutesy moniker. Rather, it comes from the technical names of a pair of spike protein mutations common to the subvariants, according to the Infectious Diseases Society of America (IDSA).

“It seems it is less [infectious] compared to JN.1, but it’s more immune-evasive,” Michael said. “Something is going on there, which we don’t know exactly.”

So far, the CDC hasn’t identified symptoms specific to FLiRT infection. Keep an eye out for these traditional COVID-19 symptoms: 

• Congestion or runny nose
• Cough
• Diarrhea
• Fatigue
• Fever or chills
• Headache
• Muscle or body aches
• New loss of taste or smell
• Nausea or vomiting
• Shortness of breath or difficulty breathing
• Sore throat

Tirachard—Getty Images

Does the COVID vaccine protect against FLiRT variants?

KP.2 is a descendant of JN.1, the Omicron subvariant that dominated the U.S. through early spring, and its mutations have been shown to evade vaccine-induced immune protection, the IDSA says.

The 2023–2024 COVID-19 vaccines, recommended by the CDC last fall, were designed to target the Omicron sublineage XBB, which was spreading at the time. New research published in the medical journal the Lancet suggests the vaccine may not be as effective against KP.2.

Even so, Dr. William Schaffner, a professor in the division of infectious diseases at Vanderbilt University Medical Center, recommends staying up to date with your COVID-19 immunizations.

“Our currently available vaccines still do provide a notable measure of protection against these newer variants,” Schaffner tells Fortune. “This is particularly important for people who are at higher risk of getting more severe disease, should they get infected.”

Along with adults 65 and older, people with the following conditions are at high risk of severe COVID-19 infection and may need additional vaccine doses, per the CDC:

• Cancer
• Chronic kidney, liver, or lung disease
• Cystic fibrosis
• Dementia or other neurological conditions
• Diabetes (types 1 or 2)
• Disabilities
• Heart conditions
• HIV
• Immunocompromised condition or weakened immune system
• Mental health conditions
• Overweight and obesity
• Physical inactivity
• Pregnancy
• Sickle cell disease or thalassemia
• Smoking (current or former)
• Solid organ or blood stem cell transplant
• Stroke or cerebrovascular disease
• Substance use disorders
• Tuberculosis

The upcoming 2024–2025 vaccines may be formulated to offer better protection against FLiRT variants. Michael adds that people who’ve already been infected by JN.1 will likely have natural cross-immunity against these variants.

“That is keeping a check on why we are unlikely to get big waves (of infections),” Michael said.

Will FLiRT variants cause a summer COVID surge?

While each of the FLiRT variants has increased its share of U.S. cases this spring, weekly test positivity percentages have steadily decreased since January.

Summertime means traveling and increased gatherings for many, and while there’s no need to panic about FLiRT variants, Schaffner says, continued vigilance about public health practices such as hand-washing and masking around vulnerable people will help keep the virus at bay.

“COVID, although it has diminished over time, it’s still out there, smoldering,” Schaffner says. “These newer variants continue to be contagious and they continue to cause illness. COVID does not disappear during the summer the way flu does.”

Michael echoes, “You will get an upsurge in cases, maybe, but you don’t reach the kinds that we saw last summer or the summer before.”

Nationwide monthly COVID-19 hospitalization rates have consistently declined since December, CDC records show, and weekly death rates have been diminishing since mid-January. These data point to FLiRT variants causing less severe infection than variants past, Michael says.

“At this stage, the virus is just trying to persist,” Michael says. “It doesn’t want to kill people—that would be the end of the virus itself. It’s just trying [to] find a way to keep itself transmitting.”

For more on COVID-19: 

• New COVID vaccines are here. What to know about 2024–25 shots as summer surge continues
• COVID can cause mental illness—but being vaccinated helps, new study shows
• The summer COVID surge has arrived. Here’s the latest on symptoms and treatment
• Got late-summer travel plans? Here’s where COVID cases are spiking in the U.S.