LB.1 is the latest COVID-19 subvariant to make headlines as it circulates in the United States. The highly contagious strain, which emerged shortly after the “FLiRT” variants, including KP.3 and KP.2, is causing an increasing proportion of infections.
As the U.S. sees an uptick in cases and emergency room visits around the country, some are concerned about a summer wave.
LB.1 is the third-leading COVID-19 variant in the U.S. right now, trailing close behind the dominant KP.3 and KP.2, according to the latest data from the U.S. Centers for Disease Control and Prevention.
As of June 22, KP.3 accounts for an estimated 33% of cases in the U.S. The next most common variant is KP.2, which makes up about 21% of cases, followed by LB.1, which is driving 17.5% of cases.
Since the end of May, the share of cases caused by LB.1 has more than doubled, per CDC data. According to some experts, this new mutated variant may be on track to surpass the FLiRT variants in the coming weeks.
While overall COVID-19 numbers, including hospitalizations and deaths, are relatively low compared to the winter, it’s clear that the virus is on the rise. Is the country facing a summer surge?
Here’s what we know about summer COVID-19 trends and the new LB.1 variant so far.
Is there a summer surge?
In recent weeks, cases have been on the rise in most U.S. states, especially in the West. The CDC estimates that as of June 25, COVID-19 cases are growing or likely growing in 44 states, stable or uncertain in 5 states, and declining in one state, Hawaii.
“As of now (early July), we’re not seeing any major nationwide surge in cases, but cases are moving up in some places and steady in others,” Andrew Pekosz, Ph.D., virologist at Johns Hopkins University, tells TODAY.com. The country is likely in the beginning of a wave, Pekosz adds, but it’s still too early to tell how summer COVID-19 trends will unfold.
Test positivity was at 8% as of June 22, per the CDC, up 1.4% from the previous week but lower than a peak of 12% in the winter. A CDC map shows that test positivity is highest in California and the Southwest U.S.
Viral activity in wastewater is “low” nationally, whereas it was “high” or “very high” for most of the winter. (The CDC no longer tracks the total number of new COVID-19 cases in the U.S.)
According to Dr. William Schaffner, professor of infectious diseases at Vanderbilt University Medical Center, what we’re seeing now is more of an expected “bump.” Unlike influenza, COVID-19 is not seasonal and continues to spread in the summer, but these bumps are far less substantial than winter surges, Schaffner adds.
As summer vacation travel peaks and people increasingly gather indoors in the air conditioning to escape heat waves, COVID-19 is expected to keep rising. “If it hasn’t bumped in your community yet, it probably will after all the July Fourth travel,” says Schaffner.
What is LB.1?
LB.1 is part of the omicron family — the newest great grandchild, so to speak, says Schaffner. The LB.1 subvariant is an offshoot of JN.1, which was dominant for most of the winter and spring.
“LB.1 is closely related to the FLiRT variants, but it has a couple of unique mutations in different parts of the spike protein,” says Pekosz. These include key mutations that affect LB.1’s ability to evade immunity.
“We’ve seen mutations like this before with other variants (including JN.1). … They don’t seem to be particularly concerning or a sign that the virus has changed drastically,” Pekosz adds.
The emergence of LB.1 continues an ongoing trend, the experts note. The SARS-CoV-2 virus mutates and gives rise to new variants, which are better able to escape immunity and outcompete other strains until a new one emerges.
More than 97% of people in the U.S. have natural or vaccine-induced antibodies against COVID-19, but this fades over time, per the CDC.
Is LB.1 more transmissible?
A characteristic of omicron subvariants is that they are very transmissible. “LB.1 highly contagious, and it is spreading very readily,” says Schaffner.
How does LB.1 compare to other new strains? “It’s too soon to tell, but so far, there is no signal that it is more transmissible than the FLiRT variants,” Dr. Bernard Camins, medical director of infection prevention at Mount Sinai Health System, tells TODAY.com.
“It may be more likely to escape immunity gained from infection or the vaccine, but it hasn’t shown that it’s more dangerous than previous subvariants,” says Camins.
The recent increase in cases appears to be driven by a combination of new variants, including LB.1 and the FLiRT strains. However, decreases in testing and genomic surveillance make it challenging to accurately track the virus. “It’s becoming harder for us to get a good sense of how quickly a variant is increasing,” says Pekosz.
What are the symptoms of LB.1?
LB.1 does not seem to be causing any distinct or new symptoms and there is no indication that it produces more severe disease, the experts emphasize.
The symptoms of LB.1 are very similar to those caused by the FLiRT variants, which include:
- Sore throat
- Cough
- Fatigue
- Congestion
- Runny nose
- Fever or chills
- Headache
- Muscle aches
- New loss of sense of taste or smell
- Nausea or vomiting
- Diarrhea
The newer strains appear to be producing generally milder infections, says Schaffner.
“Some people can still experience severe symptoms, enough to hospitalize them,” says Camins — namely, high risk groups: people age 65 and older, people with underlying medical conditions, and individuals who are immunocompromised.
Emergency room visits have increased by 23% in the past week, but are still relatively low, and hospitalization rates remain at a steady level, per the CDC.
Antivirals such as Paxlovid are effective against LB.1 and other recent strains, Schaffner notes.
Do vaccines protect against LB.1?
“The current vaccine will offer protection against severe disease,” says Schaffner. Right now, the updated 2023–2024 COVID-19 booster targeting the XXB.1.5 strain is still available. The CDC recommends high-risk groups get an additional dose.
The updated 2024–2025 vaccine to be released this fall is also expected to offer protection, the experts emphasize. “LB.1 is closely related to KP.2, which looks like it’ll be the strain targeted in the vaccine for this coming fall season,” says Pekosz.
“Previous data show that even if the vaccine doesn’t exactly match what’s circulating, there is cross-reactivity that gives you some protection,” says Camins.
The experts encourage everyone who is eligible to get an updated 2024–2025 COVID-19 vaccine this fall.
Guidelines on testing and isolation in 2024
If you develop COVID-19 symptoms or have an exposure, get tested, the experts emphasize. Testing is an important tool to protect yourself and prevent the spread of the virus.
PCR and antigen tests will detect LB.1 and other new variants, Camins notes. If you use an antigen test, follow FDA recommendations to avoid a false negative result.
The CDC recommends people who test positive stay home while sick and avoid contact with others. According to the current isolation guidelines, people can return to normal activities only after they have been fever-free (without medication) and symptoms have been improving for at least 24 hours.
“If you’re in a high-risk group and you test positive for COVID-19, we would give you Paxlovid to prevent severe illness,” says Schaffner.
How to protect against LB.1 variant
As COVID-19 cases keep rising this summer, consider taking additional steps to protect yourself and others. The CDC recommends people:
- Stay up to date with COVID-19 vaccines.
- Wear a mask in crowded, indoor spaces.
- Practice good hand hygiene.
- Cover coughs and sneezes.
- Improve ventilation.
- Practice social distancing.
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