Noah McCrory
More than a third of COVID-19 cases in the U.S. are now estimated to come from a fast-growing new member of a group of variants called “FLiRT,” nicknamed for their small but distinct changes from JN. 1 variety. JN.1 was the variant behind this past winter wave of infections.
The largest of these, called KP.2 by scientists, has multiplied rapidly in recent weeks to become the now dominant new strain of COVID-19.
According to the Centers for Disease Control and Prevention’s weekly report variant estimates, KP.2 and another strain with the same FLiRT mutations, called KP.1.1, together account for 35.3% of infections this week. This represents an increase from 7.1% in the previous month.
“This means that although KP.2 is proportionally the most predominant variant, it is not causing an increase in infections as transmission of SARS-CoV-2 is low,” a CDC spokesperson told CBS News in a statement.
The strain also shows no major worrisome changes, unlike some previously highly mutated variants that have raised alarm in recent years.
However, the rapid change in circulating variants has resulted in the Food and Drug Administration this week delaying a key step in its process of choosing the strain to target for this fall’s COVID-19 vaccines, citing the need for more “up-to-date” data.
Although federal requirements for hospitals to report COVID-19 data to authorities expired This month, the CDC says it still has reliable numbers from sources like wastewater testing and emergency rooms to continue tracking activity of the virus.
Here’s the latest on COVID-19 variants in the U.S.
What is the current new variant of COVID-19?
According to the latest projections published by the CDC, about 28.2% of COVID-19 cases nationwide are now caused by a sublineage of the virus called the KP.2 variant.
The next biggest variant on the rise is another JN.1 descendant called JN.1.16. This strain has not grown as quickly, only increasing to about 10% of cases this week.
This projection is based on genetic sequences of the virus reported primarily by public health labs, which have declined significantly in recent weeks along with the slowdown in overall case numbers. Other CDC data from residual waters It is traveler the test still does not separate KP.2 from its parent JN.1.
KP.2 is a closely related descendant of JN.1 variant of last winter, which ended not be significantly more serious than the variants that were dominant before it, despite their large number of mutations.
“So it’s something that we’re watching. It’s something that we’re monitoring. And again, we reiterate the need for continued surveillance of SARS-CoV-2 in people around the world so that we can monitor this evolution,” said the World Health Organization. Maria Van Kerkhove told reporters Wednesday.
Why are these COVID-19 variants called FLiRT?
The FLiRT moniker comes from two distinct mutations observed in several descendants of the JN.1 variant that emerged around the world following its spread during the winter. Some of the largest strains with FLiRT mutations in the US currently are KP.2 and KP.1.1.
“It’s essentially just forming a word with the specific amino acid changes in the spike protein F456L + R346T, or phenylalanine (F) to leucine (L) at position 456 and arginine [R] for threonine [T] at position 346,” Canadian biologist Ryan Gregory, a professor at the University of Guelph, told CBS News in an email.
Gregory coined this nickname in March, and has gained traction among variant trackers who have detected and dubbed many distinct changes in the virus during the pandemic. Although unofficial, these nicknames have become commonly used names for a number of variants.
FLiRT has won another nickname – “tiLT” variants – which was coined by Australian consultant Mike Honey. FLiRT refers to a collection of faster-growing JN.1 branches that trackers are keeping an eye on, among them KP.2.
“Basically, virtually everything now is descended from BA.2.86.1.1 (JN.1) and things are evolving quickly, so it makes more sense to focus on mutations of interest rather than individual variants for now,” Gregório wrote.
Do FLiRT variants lead to different COVID-19 symptoms?
Unlike some previous highly mutated variants that raised concerns about possible changes in symptoms In recent years, the JN.1 variant that many Americans have likely already caught during the winter is closely related to the KP.2 strain now on the rise.
“Based on current data, there are no indicators that KP.2 can cause more severe illness than other strains,” a CDC spokesperson told CBS News.
The two distinct mutations called FLiRT of KP.2 have also been seen before, in XBB.1.5 variants that circulated throughout 2023, the spokesperson said.
A draft to study of scientists in Japan, released as a preprint that has not yet been peer-reviewed, found that the variant appeared to dodge antibodies better than the JN.1 variant. This “increased immune resistance” likely explains its rise, the scientists said.
In general, health authorities and experts have minimized claims that the variants were causing different symptoms. Changes in a person’s immunity due to vaccines and previous infections often play a role in different symptoms rather than specific mutations.
“Mutations happen frequently, but only sometimes change the characteristics of the virus,” the CDC said it says.
Will the vaccines work against the FLiRT variants?
The CDC has not made any changes to its current vaccine recommendations, which have been Last update in April. But the emergence of these new descendants of the JN.1 variant, like KP.2, could affect which vaccine the FDA chooses for next fall and winter.
Most Americans remain eligible to receive at least one dose of last season’s updated COVID-19 vaccine, which the CDC data so far suggests it was up to 51% effective against emergency room or urgent care visits during a period when JN.1 was on the rise.
“CDC will continue to monitor community transmission of the virus and the performance of vaccines against this strain,” the agency said of KP.2.
Last month, experts from the World Health Organization recommended for vaccine manufacturers to produce shots targeting the JN.1 variant for the next season. The FDA’s own panel of vaccine experts was scheduled to evaluate this approach for the American vaccine market next week.
However, the agency recently announced decided to postpone the meeting until June in hopes of buying more time to ensure the choice of a vaccine target that is “most appropriate to be used for the strain(s) expected to circulate” in the fall .
“The FDA, along with its public health partners, carefully monitors trends in circulating strains of SARS-CoV-2. As has been the case since the emergence of COVID-19, we have recently observed changes in the dominant circulating strains of SARS-CoV – 2,” an FDA spokesperson told CBS News in a statement.
Pfizer has generated research data on its KP.2 vaccines, but a company spokesperson said it is currently unable to share the results. A Moderna spokesperson did not respond to a request for comment.
A Novavax spokesperson said it has data showing its fall vaccine candidate aimed at JN.1 has “good cross-reactivity” to KP.2. Although Novavax’s vaccine will take longer to produce than mRNA shots from Pfizer and Moderna, the spokesperson said the FDA’s delay in the meeting “will not affect” its ability to administer a shot this fall.
“We produced JN.1 in accordance with recommendations and are on track to deliver an updated vaccine this fall,” said the Novavax spokesperson.
