A new variant of COVID-19 called KP.3 is on the rise in the U.S. and has been detected in Arizona.
The variant of the SARS-CoV-2 virus that causes COVID-19 comprised 25% of the COVID-19 cases in the U.S. for the two-week period ending June 8, up from 3.6% for the two weeks ending April 27, according to estimates from the Centers for Disease Control and Prevention.
“CDC predicts that KP.3 is growing and will become the most common SARS-CoV-2 lineage nationally,” a CDC spokesperson wrote in an email Tuesday. “CDC is working to better understand its potential impact on public health.”
Though KP.3 has been increasing in prevalence across the country, circulation of the SARS-CoV-2 virus remains relatively low as are hospitalizations and deaths due to COVID-19, federal and state data show.
“Most key COVID-19 indicators are showing low levels of activity nationally, therefore the total number of infections this lineage may be causing is likely low,” the CDC spokesperson wrote. “COVID-19-associated hospitalizations and deaths remain lower than at any time since March 2020.”
Here are seven things to know about KP.3:
It is related to the FLiRT strains of COVID-19
KP.3 is technically not one of the FLiRT variants, which were previously dominant in the U.S. in the spring, according to Andrew Pekosz, professor and vice chair of the Department of Molecular Microbiology and Immunology at the Johns Hopkins Bloomberg School of Public Health.
“It has mutations similar to the FLiRT mutations, they are just different abbreviations,” Pekosz wrote in an email.
But KP.3 and the FLiRT versions are related. Like other strains of the COVID-19 virus, they are descendants of the JN.1 variant, which emerged during the winter of 2023-24 and is descended from the omicron variant that was first detected in late 2021. The severity of infections caused by JN.1 does not appear to be any worse than earlier strains.
Omicron variants have the same characteristics: They seem to spread easily and evade antibodies built up from vaccinations and previous infections, which is why new subvariants keep surfacing.
“Any of those that have that KP designation are in the FLiRT family,” said David Engelthaler, who leads the infectious diseases division of the Arizona-based Translational Genomics Research Institute. “These are part of the same lineage that come off the same branch of the family tree.”
It’s not expected to cause a summer surge of COVID-19
“It looks like a summer wave is very modest and while KP.3 may drive some new cases, it doesn’t look right now that it will drive a significant summer surge,” Pekosz wrote,
There does appear to be an increase in COVID-19 cases in the Western U.S., including in Arizona, right now, but there’s no increase in hospitalizations and deaths, Engelthaler said. He said he’d be surprised if there is a “noticeable” increase in illness due to KP.3 during the next few months.
New COVID-19 vaccines anticipated for fall should provide protection
The U.S. Food and Drug Administration’s Vaccines and Related Biological Products Advisory Committee on June 5 unanimously voted to recommend a monovalent COVID-19 vaccine for the fall that targets JN.1. The CDC and the Advisory Committee for Immunization Practices will discuss and vote on the recommendations June 27.
KP.3 has a few mutations compared to JN.1 but it is close enough that a JN.1 vaccine “should provide good protection against KP.3 and other FLiRT variants,” Pekosz wrote.
By the time the new vaccines hit, there will likely be new subvariants circulating and “protection is not really going to be against the strain that it was developed for,” but there is still some level of protection, Engelthaler said.
“Probably the greatest amount of protection is going to be for people who have not been vaccinated recently in the last year or who have not had an infection in the last year,” Engelthaler said. “Those that are high risk that have not had a recent vaccination or infection are going to get the most benefit from it.”
About 12 cases of KP.3 have been detected in Arizona
In a search of an internationally shared database called GISAID (Global Initiative on Sharing All Influenza Data), Engelthaler says he found about 12 cases of KP.3 in Arizona going back as far as early May.
The number 12 is likely a small fraction of the true number of KP.3 cases in Arizona. The amount of viral sequencing of positive tests that’s happening in the state is much lower than it was during the COVID-19 pandemic, Engelthaler said.
“It’s probably quite a bit more than that,” he said of the KP.3 prevalence in Arizona. “We’ve seen it show up in multiple counties. … We seem to be tracking the same trends as what’s seen nationally.”
It’s unclear if KP.3 causes long COVID
Recent research suggests COVID-19 caused by subvariants of omicron are less likely to result in a long COVID infection, Engelthaler said.
“This version of the virus, all the omicron variants, don’t really like the lower lung cells and they don’t disseminate as much as the earlier variants that we saw with COVID during the pandemic,” Engelthaler said. “That is good news. We’re likely to see less long COVID outcomes, though that’s a very difficult thing to know for sure.”
The CDC defines long COVID as a chronic condition that occurs after an infection with the virus that causes COVID-19 and is present for at least three months. The condition includes a wide range of symptoms or conditions that may improve, worsen, or be ongoing, the CDC says.
Pekosz said that long COVID remains a risk with KP.3 and other variants.
JN.1 and its descendants haven’t been around long enough to have documented long COVID cases and “there is nothing about its sequence or the illness that it causes that would make me believe that long COVID isn’t possible after a JN.1 infection,” he wrote.
If you have symptoms, follow the CDC’s updated COVID-19 guidance
New CDC guidance for COVID-19 now aligns with guidelines for other common respiratory viruses.
The guidance is to stay home and away from others (including people you live with who are not sick) if you have respiratory virus symptoms that aren’t better explained by another cause. The symptoms can include fever, chills, fatigue, cough, runny nose, and headache, among others.
The CDC advises going back to normal activities when, for 24 hours, both of the following are true:
- Your symptoms are getting better overall.
- You have not had a fever (and are not using fever-reducing medication).
Anyone going back to normal activities should take added precautions over the next five days following their illness, with steps like masks, physical distancing, and/or testing when you will be around other people indoors, the CDC says.
The COVID-19 virus continues to mutate and is unlikely to go away
While cases, deaths and hospitalizations have decreased significantly since the COVID-19 pandemic, it continues to cause hospitalizations and deaths, including among Arizonans. People with compromised immune systems, including elderly individuals, are at higher risk.
“There’s a good chance that we will all continue to get COVID. Immunity doesn’t last, primarily because the virus just keeps changing,” Engelthaler said. “It’s kind of a Whac-A-Mole game. As soon as we develop some immunity or a new vaccine, the virus has already changed and it’s going to be something else popping up.”
Reach health care reporter Stephanie Innes at Stephanie.Innes@gannett.com or at 480-313-3775. Follow her on X, formerly known as Twitter, @stephanieinnes.
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